Clinical Correlates in Patients with Elevated Platelet-Associated Immunoglobulins*!"

Transcription

1 ANNALS O F CLINICAL AND LABORATORY SCIENCE, Vol. 18, No. 1 Copyright 1988, Institute for Clinical Science, Inc. Clinical Correlates in Patients with Elevated Platelet-Associated Immunoglobulins*!" MARK SZAL, B.A. and NEIL BLUMBERG, M.D. Blood Bank, Strong Memorial Hospital and Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY ABSTRACT Studies are reported pertaining to platelet-associated IgG (PAIgG) and IgM(PAIgM) in patients with thrombocytopenias considered possibly immune-mediated on clinical grounds. Approximately 14 percent of all patients with these disorders had elevated PAIgM but normal levels of PAIgG. O f patients with classic autoimmune throm bocytopenia (ITP), there was a trend toward more frequently normal levels of PAIgG in chronic ITP compared with patients with acute ITP, but this was not statistically significant. Patients with acute ITP had higher levels of PAIgG and PAIgM in general than those with chronic ITP. Patterns of PAIgG and/or PAIgM elevation were not significantly different when chronic and acute ITP were compared, nor when childhood ITP was compared with adult ITP. Patients with immune thrombocytopenias owing to malignant disorders were likely to have lower levels of PAIgG compared with those w ith classic ITP. Treated patients with im m une throm bocytopenias showed a trend toward earlier response to therapy if they had only elevated PAIgG as opposed to elevated PAIgM alone or elevated PAIgM and PAIgG (p = 0.17). There appear to be great overlaps in the patterns and quantities of PAIgG and PAIgM in patients with immune-mediated thrombocytopenias in widely varied clinical settings. This suggests some underlying common pathophysiologic mechanisms for throm bocytopenia in these clinically diverse disorders. It is believed that the data are most consistent with the hypothesis that thrombocytopenia in patients with elevated PAIgG and/or PAIgM is most probably of immune origin even in such diverse disorders as systemic lupus erythematosus, cirrhosis of the liver, lymphoma, leukemia, cancer, or septic conditions, as well as in ITP. Introduction Over the past decade, sensitive and relatively simple laboratory tests have been developed for measuring plateletassociated im m unoglobulins and com /88/ $01.50 Institute for Clinical Science, Inc. * Supported in part by Dynatech Laboratories, Inc., Chantilly, VA and HHS grant HL from the National Institutes of Health. t Send reprint requests to Neil Blumberg, M.D., Box 608, University of Rochester Medical Center, Rochester, NY

2 p le m e n t c o m p o n e n ts th a t m e d ia te im m une destruction of these cells. 6,9 Many questions remain concerning the interpretation of these tests and their role in explaining the pathophysiology of throm bocytopenia in a wide variety of clinical circumstances. 10 However, there is little doubt that in most patients with idiopathic throm bocytopenic purpura (ITP) the mechanism of platelet destruction is largely immune, and that in 80 to 90 percent of these patients elevations of cell surface IgG can be dem onstrated. 6,9 Nonetheless, autoimmune thrombocytopenia has rem ained a clinically based diagnosis in which the role of platelet antibody tests is controversial. It is believed that the presence of increased amounts of platelet-surface immunoglobulins and/o r com p lem en t can be of potential clinical significance regardless of the pathophysiologic m echanism s involved. However, the amount of platelet-associated im m une com ponents is only one of several factors which determine the fate of these peripheral blood cells in immune-mediated disease. One critical factor is the avidity with which the monocyte-macrophage network (reticuloendothelial system) recognizes and destroys cells with increased amounts of surface immunoglobulins. 8 Because it is not certain whether the finding of elevated platelet-associated immunoglobulins in throm bocytopenic patients is a specific marker for immune destruction or can be non-specific, it would be of interest to compare the levels and patterns of surface IgG and IgM in patients with diverse disorders complicated by thrombocytopenia. To assist in the evaluation of thrombocytopenic patients, our laboratory perform s assays of p la te le t surface IgG (PAIgG) and IgM (PAIgM). A retrospectiv e c lin ic a l re v ie w of p a tie n ts is reported and is intended to address a n u m b er of questions. It would be of interest to know whether differences in CLINICAL ASPECTS O F ELEVATED PAIgG/IgM 25 the pattern of PAIgG and PAIgM correlated w ith response to tre a tm e n t in patients with im m une throm bocytopenia. Since many patients with thrombocytopenias of questionable im m une origin also have increased PAIgG and PAIgM, patients w ith classical IT P were evaluated to see whether they differed from o th er th ro m bocy to penic patients in the quantitative or qualitative pattern of IgG and IgM on their platelets. Because adult and childhood ITP differ sig n ificantly in th e ir clin ical course, with children having a lower incidence of chronic ITP, the pattern of elevated PAIgG and PAIgM in these two groups was examined. It is hoped these data might shed light on possible differences in pathophysiology, and also provide information of potential prognostic utility, as has been the case in the area of red cell immunology. Methods of Analysis P a t ie n t s This study was a retrospective medical record review of patients who had samples evaluated for PAIgG and PAIgM during the two year period 1984 to P atien t sam ples w ere re fe rre d from approximately 1 0 different hematologists practicing at five different hospitals in our area. Obviously, this population of patients is highly biased towards patients in which the practitioner felt there was a high a priori likelihood of an immune mechanism. Information about patient age, sex, clinical diagnosis, date of diagnosis, duration of illness (days to platelet counts greater than 50,000 and 100,000), bone m arrow exam, com plete blood counts, tests for red cell or other autoimm unity or immunological param eters, treatment employed, duration of treatm ent, and serial platelet counts after diagnosis were collected. Many patients had incomplete information or foliowup.

3 26 SZAL AND BLUMBERG Any history of malignancy, autoimmune disease, coagulopathy, recent viral illness, blood pro duct transfusion, and recent drug use were also noted. Many patients, especially children, received no specific therapy for their thrombocytopenia. Tests for circulating im m une complexes were only rarely performed; PAIgG and PAIgM as determ ined by our laboratory were recorded. Unless otherw ise noted, all patients had platelet counts <150,000 per xl at the time of testing, although several were rapidly recovering and had normal counts within a few days after sampling. Patients were classified in the classic ITP group if they had an initial platelet count of < 1 0 0, per j u l I, normal physical examination except for signs related to thrombocytopenia, normal laboratory findings, and the clinical picture was not complicated by recent drug use, autoimm une disease, concurrent malignancy, sepsis, pregnancy or trauma. All patients in the classic ITP group met the criteria proposed by Kelton for probable ITP, with the vast majority having bone marrow exam inations. 9 Most of these patients also m et the criteria for definite ITP once the results of therapy or clinical course were evaluated. 9 Only eight of patients, all with severe hem orrhage, received platelet transfusions. None of the patients classified as having classic ITP were transfused. O ther patients with elevated PAIgG and/or PAIgM were classified according to th e ir prim ary diagnosis, such as autoimmune disease, malignancy, infection, etc. These groups and those with classic ITP were compared by their pattern of test results in each of four categories: (1) E levated PAIgG and norm al PAIgM; (2) Normal PAIgG and elevated PAIgM; (3) Both elevated; and (4) Both normal. Patients in each of these categories were then subdivided into adults versus children ( 1 2 years old or less at date of diagnosis), acute versus chronic (>six m o n th d u ra tio n o f p la te le t c o u n t <100,00 per xl) classic ITP versus o th er diagnoses (sepsis, m alignancy, pregnancy, other autoim m une, drugrelated, or trauma), and time from diagnosis to remission (defined as platelet count > 1 0 0, p er jl1), and finally treatm ent versus no treatment. In order to see if the level of elevated PAIgG was of prognostic significance or differed in the various groups, patients with elevated PAIgG were further placed in one of four categories, ( to ; 20.1 to 50.0; 50.1 to 100.0, or ) dependent on level of PAIgG (normal is <10 fg per platelet in soluble IgG equivalents). A similar analysis was performed for PAIgM levels. S t a t is t ic a l A n a ly sis All analyses were carried out using a microcomputer* and softw are.t Comparison of frequencies of events was perform ed using C hi-square contingency tables, with individual frequencies being further compared to each other employing Fisher s exact test. It was recognized that the performance of these multiple comparisons could lead to statistically significant findings merely on a probabilistic basis (i.e., one in 2 0 comparisons). Thus, results of statistical significance derived from m ultiple 2 by 2 contingency tables and F ish e r s exact test should be view ed w ith caution. An exploratory study such as this requires something of a fishing expedition statistically and is intended to point toward further useful comparisons in larger and better controlled studies. * Apple Macintosh (Cupertino, CA). t NCSS: Dr. Jerry L. Hintze, Utah State University, Kaysville, UT.

4 Laboratory Techniques I n t r o d u c t io n a n d P r in c ip l e s The assay for PAIgG has been p reviously described. 1 Soluble IgG standards or PAIgG com pete w ith solidphase IgG for binding to an alkaline phosphatase-linked anti-igg antiglobulin reagent. The principle of the assay is that increased concentrations of soluble IgG or PAIgG will compete for anti-igg and reduce anti-igg binding to the solidphase IgG. This assay can reproducibly detect changes of about 50 molecules per platelet of IgG. Results are reported in fg per platelet in soluble IgG equivalents (normal = 0 to 10). Whole platelets are employed so that measurements reflect only surface PAIgG and PAIgM. The assay for PAIgM is essentially similar except that the assay does not use soluble IgM as a standard curve. P r o c e d u r e f o r PAIgM A ssay, I n c l u d in g R e a g e n t s, S o l u t io n s a n d A p p a r a t u s Immulon II m icrotiter plates^ were washed three times using distilled water. A m urin e m onoclonal antibody th at reacts with an undefined antigen present on all hum an platelets (UR produced by the Laboratory Medicine Division Hybridoma Facility) was added to each well in the amount of jjli at a concentration of approxim ately 1 0 xg p er ml in coating buffer (1.59 g per L Na2C 0 3, 2.93 g per L N ah C 03, ph 9.6). The plate was then incubated for two hours at 37 C, then overnight at 4 C. The antibody was used as crude mouse ascitic fluid. Platelets were first sedim ented and resuspended in PBS-EDTA (0.01 M Na2 HP 0 4/NaH 2P0 4, 0.15 NaCl, 3 g per L Na2EDTA, ph 7.0) prior to $ Dynatech, Chantilly, VA. CLINICAL ASPECTS OF ELEVATED PAIgG/IgM 27 adhering to the plate. After resuspension in PBS-EDTA at a count of 370,000 per xl, a 100 xl aliquot of platelets was added to each of two wells for each sample to be tested. After platelets have been added, the m icrotiter plate was centrifuged at 1800 RPM in a GLC-4 centrifuge for 1 0 minutes to sedim ent the platelets onto the monoclonal antibody coated surface. The plate was then incubated at room tem perature for 50 minutes. It was then washed semi-automatically, without need for centrifugation, three times utilizing PBS (ph 7.2) and a Mini-Wash. $ One hundred xl of PBS-1 percent bovine serum albumin were added to each well to reduce nonspecific adsorption of enzyme-antiglobulin conjugate during a subsequent step. This required a 30 minute room temperature incubation, and was followed by two further washes with PBS-1 percent BSA. One hundred xl of alkaline phosphatase lin ked to affinity-purified a n tihuman IgM (Sigma) were added at a dilution previously optimized to the lot in question. The conjugates were usually employed at 1:800 or 1 : dilutions. Two wells received no conjugate to serve as negative controls for non-specific binding by the anti-igm-enzyme conjugate. A further incubation at room temperature for 60 minutes was performed, followed by three PBS-1 percent BSA washes. Substrate, one mg per ml paran itro p h e n y l p h o sp h a te in M Na2C 0 3, M MgCl2, ph 9.8 was added at 100 xl per well. Color developm ent was measured spectrophotometrically 17 w ith a MR600 m icrotiter plate reader^ coupled to an Apple He microcomputer for which kinetic-elisa programs have been written. H At this stage, BSA, BCA, W est Chester, PA. II Sigma. f Dr. Jonathan Cowles, Pittsford, NY

5 28 SZAL AND BLUMBERG AA405nm per minute X 1000 was computed by least squares linear regression of absorbance readings taken at 20, 25, 30, and 35 minutes after substrate addition. The correlation coefficient for the linearity of the AA405nm versus time was usually 0.99, thus confirm ing the m easu rem en t of first-o rd er enzym e kinetics, which has been shown p reviously to correlate linearily with the am ount of im m unoglobulin and antiimmunoglobulin bound. The assay was linear throughout the range used. 17 The amount of IgM bound to the solid-phase platelet layer was reported as the mean of th e d u p lic a te d e te rm in a tio n s of AA405nm p e r m in u te X The duplicates were usually within 1 0 to 2 0 percent. Because the kinetic m easurem en t of enzym e activity is m ade at ambient tem perature, controls were run to normalize the results from day to day. N o r m a l R a n g e The IgM bound to platelets of nonthrombocytopenic hospitalized patients yielded a norm al range of for AA405nM per minute X 1000 (mean + 2 S.D., n = 268). D is c u s s io n, S o u r c e s o f E r r o r a n d I n t e r p r e t a t io n As in previous reports, clinical review su g g ested th a t 80 to 90 p e rc e n t of patients with classic ITP have elevated levels of PAIgG in our assay. 1 Likewise, normal levels of PAIgG in our experience with over patients usually suggested a non-immune etiology for the thrombocytopenia. Artifactual causes of falsely norm al PAIgG in throm bocytopenic patients known to have ITP include the early beneficial effects of therapy, the onset of clinical remission, and recent platelet transfusions. In our experience, falsely elevated levels in thrombocytopenia were restricted to conditions of rapid platelet destruction and the elevations were modest (e.g., 1 0 to 2 0 fg per platelet of IgG). About five to 10 percent of non-throm bocytopenic hospitalized patients also had elevated levels, the vast majority in the lower end of this range. This latter finding was partially due to in te n tio n a l defin itio n of th e norm al range as excluding the upper 2.5 percent of normals in the Gaussian distribution, and partially due to the slightly skewed distribution of PAIgG and PAIgM that was typical of most biological measurements. Results Over the last two years 176 samples from patients with thrombocytopenia or a history of a thrombocytopenic illness w ere te ste d by the p re se n t authors. Most of these patients were suspected of having ITP or im m une throm bocytopenia owing to their underlying primary disease, such as lupus or lym phom a. Some of these patients were known to be in remission from ITP, and some were known to have non-immune thrombocytopenia. O f these tests, 49 of 176 showed normal levels of both PAIgG and PAIgM. O f those with elevated platelet surface immunoglobulins, 18 of 127 (14 percent) had elevated PAIgM only, 44 of 127 (35 percent) had elevated PAIgG only, and 65 of 127 (51 percent) had elevated levels of both immunoglobulins. Based upon availability of medical records and likelihood of adequate tim e for followup, patients were chosen for investigation whose samples were received prior to mid-1986 and who had been seen in our local area. A total of 110 patients were investigated; of these, 15 were excluded from the analysis because the initial platelet counts were found to be spurious or because the throm bocytopenia was m ild and platelet counts did not drop below 1 0 0, O f the 95 patients remaining, 48 had probable classic ITP. Of the 47 thrombocytopenic patients without classic ITP

6 whose platelets were tested for PAIgG and PAIgM, eight had a solid tumor, six were pregnant but not thought to have classic ITP, six had systemic lupus erythematosus, six were septic, six had leukemia, five had lymphoma, three had possible drug induced throm bocytopenia, three had myelodysplastic syndromes, and one each had aplastic anemia, sickle cell crisis, cirrhosis of the liver, or post-surgical thrombocytopenia. Of the 48 patients with classic ITP, eight had insufficient follow up (< 6 months) to classify as acute or chronic, and two others were not tested for levels of PAIgM owing to insufficient blood sample. Of the 10 patients who had elev ated values for n e ith e r PAIgG or PAIgM, seven were entering remission at the time the test was run, and three were chronic ITP patients who continued to have a low platelet count. The 31 patients with active disease could be grouped as shown in table I. None of the 14 acute ITP patients had both PAIgG and PAIgM s that were normal, as compared with three of 17 of those who had chronic ITP (p = 0.15). There were no differences in pattern of elevated PAIgG and/or PAIgM between those with acute or chronic ITP. B ecause of th e fin d in g of norm al values of PAIgM and PAIgG in a few patients with chronic ITP, the amount of PAIgG was examined in the 42 patients TABLE I Patterns of Platelet-Associated IgG and Platelet-Associated IgM in Acute or Chronic Classic Autoimmune Thrombocytopenia Group Acute Chronic Elevated PAIgG only 7 (50%) 6 (29%) Elevated PAIgM only 0 (0%) 1 (5%) Both elevated 7 (50%) 7 (33%) Neither elevated* 0 (0%) 3 (33%) Total 14 (100%) 17(100%) *Seven patients, four with chronic autoimmune thrombocytopenia and three with acute autoimmune thrombocytopenia were in recovery phase and had normal PAIgG and PAIgM at the time of testing and are not included in the table. CLINICAL ASPECTS OF ELEVATED PAIgG/IgM 29 TABLE I I Levels of Platelet-Associated IgG in Patients with Chronic or Acute Autoimmune Thrombocytopenia Group fg fg P Chronic 9 of 19 (47%) 10 of 19 (53%) 0.5 Acute 8 of 23 (35%) 15 of 23 (65%) 0.04 P from both the classic ITP and other groups who had elevated levels of this immunoglobulin. These data are shown in table II. There was a significant trend toward higher levels of PAIgG in patients with acute immune thrombocytopenia as compared to chronic immune thrombocytopenia. Of 24 patients with elevated PAIgM whose thrombocytopenias could clearly be classified as acute or chronic, th ere was a significant tren d tow ard higher levels of PAIgM in the chronic th ro m b o c y to p e n ia s, a lth o u g h th e num bers of patients is quite small. Of the nine patients with chronic immune thrombocytopenia, only two ( 2 2 percent) had modest elevations of PAIgM in the range of (normal is = 1.36), whereas seven (78 percent) had levels > 2.00 (p = 0.03). In contrast, amongst 15 patients with acute immune thrombocytopenia, six had m odest elevations of PAIgM versus nine with levels >2.00 (p = 0.23). The patterns of PAIgG and PAIgM are shown in the 36 patients with clinically active classic ITP according to age in table III. Not included in the table are an additional five patients who had no PAIgM measurements and an additional seven patients who were adults in recovery phase of acute ITP w ith norm al PAIgG and PAIgM. None of the differences shown are statistically significant, perhaps owing to inadequate sam ple size. Two children were the only classic ITP patients with isolated elevations of IgM (two of 13) versus none of 23 adults with classic ITP with this pattern (p = 0.09).

7 30 SZAL AND BLUMBERG TABLE I I I Patterns of Platelet-Associated IgG and Platelet-Associated IgM by Patient Age in Classic Autoimmune Thrombocytopenia Group Adults Children Elevated PAIgG only 9 (39%) 6 (46%) Elevated PAIgM only 0 (0%) 2 (15%) Both elevated 13 (57%) 3 (23%) Neither elevated 1 (4%) 2 (15%) Total 23 (100%) 13 (100%) Of the 95 patients with classic ITP or other types of thrombocytopenia, 8 8 had levels of both PAIgG and PAIgM measured. To determ ine if the patterns of PAIgG and PAIgM elevations varied b etw een those w ith classic IT P as opposed to other potentially immunem ediated throm bocytopenias (malignancy, other autoimmune disease, pregnancy, sepsis, drugs, etc.), the patients were grouped as shown in table IV. No significant difference is seen betw een these two groups in PAIgG/PAIgM patterns. Amongst patients with elevation of PAIgG and/or PAIgM there was a trend tow ard m ore patien ts w ith increased PAIgM in patients in the other group (24 of 34, 71 percent) as compared with those with classic ITP (18 of 33, 55 percent) (p = 0.13). To assess w hether or not the quantity of PAIgG c o rrelated w ith diagnosis am ongst those w ith elevated PAIgG, those w ith classic ITP and those with o th e r diagnoses w ere d iv id ed into groups of PAIgG = 10 to 20 and PAIgG = >20. O ther patients with autoimmune disease, sepsis, drugs, etc. as the probable cause of th eir autoim m une throm bocytopenia had a similar distribution to patients with classic ITP. However, patients with malignancies (solid tumors, lymphoma, leukemia) tended to have lower levels of PAIgG compared with patients with classic ITP (table V). O f classic ITP patients with elevated PAIgG, 26 of 36 (72 percent) had elevations greater than twice the upper limit of norm al, com pared w ith five of 14 patients (36 percent) with malignancies (p = 0. 02). S im ilarly, classic IT P p atien ts w ith elev ated PAIgM w ere som ew hat m ore likely (70 percent) to have higher levels of PAIgM ( > 2.00) than patients with malignancy (50 p ercent) although this difference was not statistically significant (p = 0.28). To examine whether or not patterns of PAIgG and PAIgM c o rre la te d w ith response to treatm ent, patients w ere d iv id ed in to tre a te d and u n tre a te d groups and the num ber of patients noted w hose p la te le t c o u n t had ris e n to > 1 0 0, per (jli within 2 1 days of treatm ent initiation, or within this time after initial diagnosis if no tre a tm en t was given. R esults em ploying a p la te le t count of 3=50,000 per jl1 as the measure of response gave similar results. Most patients w ere treated with corticosteroids, but some received in addition, or alternatively, splenectomy, high dose intravenous IgG, or cytotoxic chem o therapy for their underlying disease. The results of this division of the data are shown in table VI. No statistically significant differences were found. The treated patients w ere no more likely to have platelet counts ^ 1 0 0, per jjli within three weeks (21 of 44, 48 percent) as compared with untreated patients ( 1 0 of 24, 42 percent). However, th ere is a tr e n d fo r th e p a tie n ts w ith o n ly TABLE IV Patterns of Platelet-Associated IgG and Platelet Associated IgM According to Primary Diagnosis Group Classic ITP Other Elevated PAIgG only 15 (35%) 10 (22%) Elevated PAIgM only 2 (5%) 5 (11%) Both elevated 16 (37%) 19 (42%) Neither elevated 10 (23%) 11 (24%) Total 43 (100%) 45 (100%) ITP = autoimmune thrombocytopenia

8 in creased IgG on th e ir p latelets to respond to therapy (eight of 13, 62 percent) better than those with IgM, or IgM and IgG on their platelets (nine of 23, 39 percent) (p = 0.17). Discussion O ur findings, lim ited by the retrospective m ethod which was employed, revealed few statistically significant differences in patterns or quantitation of PAIgG and PAIgM in p atien ts w ith widely differing clinical settings. This confirms the results in a much larger study by Helm erhorst and colleagues in which patients with prim ary im m une throm bocytopenia ( classic ITP ) differed little from those with secondary im m u n e th ro m b o c y to p e n ia s (e.g., cancer, lupus, etc. ). 5 Recently, Panzer and colleagues from Vienna reported virtually identical results patients with ITP differ very little, if at all, from thrombocytopenic patients with malignancy, aplasia, infection, etc. in term s of the level or patterns of platelet-associated im m unoproteins. 15 M cfarland and her colleagues have reported essentially similar findings. 12 As reported by others, failing to test for PAIgM and/or platelet associated complement components will miss perhaps as many as 15 percent of patients with probable autoimmune phenom- TABLE V Levels of Platelet-Associated IgG by Underlying Diagnosis Group fg > 20 fg Classic ITP 10 of 36 (28%) 23 of 36 (72%) Malignancy* 9 of 14 (64%) 5 of 14 (36%) Otherf 3 of 15 (20%) 12 of 15 (66%) Total 22 of 65 (34%) 43 of 65 (66%) Includes patients with solid tumors, leukemia or lymphoma i fincludes patients with sepsis, pregnancy, cirrhosis, systemic lupus, sickle cell crisis, or myelodysplastic syndrome. CLINICAL ASPECTS OF ELEVATED PAIgG/IgM 31 TABLE V I Response to Treatment According to Patterns of Platelet-Associated IgG and Platelet-Associated IgM Treated Untreated Recovered Recovered Groups < 21 days < 21 days Elevated PAIgG only 8 of 13 (62%) 2 of 5 (40%) Elevated PAIgM only 1 of 3 (33%) 1 of 1 (100%) Both elevated 8 of 20 (40%) 2 of 8 (25%) Neither elevated 4 of 8 (50%) 5 of 10 (50%) Total 21 of 44 (48%) 10 of 24 (42%) ena involving platelets. 2,4,5,1 2,1 3,1 4,15,1 6,1 8 Some of these patients with elevations only of PAIgM undoubtedly have classic ITP. It is suggested that combined tests of PAIgG and PAIgM will yield evidence for increased immunoglobulins in perhaps 95 percent of patients with active ITP. The rest presum ably rep resent instances of IgA sensitization only, or immune thrombocytopenia on the basis of increased removal of normal platelets by abnormal monocytic, lymphoid, or phagocytic effector cells. No clearcut prognostic utility for these tests has em erged from our data or those of others, 7,11 Some modest heterogeneity in the clinical course of patients with immune thrombocytopenias is suggested by the results of others and those herein reported. As noted by Helm erhorst and associates, 5 there is a trend toward normal levels of PAIgG and PAIgM in those with chronic ITP (table I). Patients with acute ITP are significantly more likely to have higher levels of PAIgG (table II). Patients with chronic ITP were significantly more likely to have higher levels of PAIgM, but the numbers of patients studied in this regard were small. There remained approximately five percent of our p atien ts w ith p ro b ab le im m une throm bocytopenia whose PAIgG and PAIgM were normal. Despite the well known clinical distinctions betw een ITP of childhood and adulthood, the patterns of PAIgG and PAIgM in these two groups were similar

9 3 2 SZAL AND BLUMBERG (table III). Likewise, patients with probable autoim m u ne thro m b o cy to pen ia owing to drugs, sepsis, malignancy, etc., did not differ in their pattern of PAIgG and IgM from those with classic ITP (table IV). Patients with malignancy as their underlying cause of autoimmune thrombocytopenia were slightly, but significantly m ore likely to have m odest elevations of PAIgG and PAIgM than those with classic ITP, who tend to have greater amounts of immunoglobulin on their platelets (table V). However, there is a great overlap in these two groups of patients. There was a trend toward more rapid response to treatm ent in patients with elevated PAIgG as their only abnormality (table VI). McFarland and associates reported that those patients with higher PAIgG levels w ere significantly more likely to achieve a corticosteroid-induced com p lete rem ission than those w ith low er levels. 12 C ourt and colleagues3 recently re p o rted that patients w ith treatment resistant immune thrombocytopenia were more likely to have normal or lower levels of PAIgG than those who responded to therapy. Some have interpreted the observed elev atio n s of PAIgG and PAIgM in thrombocytopenic patients with sepsis, malignancy, etc. as being non-specific as markers of immune destruction. It is our belief the opposite is possible. Many p atien ts w ith throm bocytopenia and non-immune primary disorders such as in fectio n, splenom egaly, cirrh o sis, cancer, etc. may nonetheless have an im m une etiology for their low platelet counts. The marked similarities between the clinically diverse groups reported in this communication could indicate that many thrombocytopenias, w hether acute or chronic, adult or pediatric, classic ITP or associated with other clinical conditions, share an underlying pathophysiology. Acknowledgments Deep appreciation is expressed to the hematologists and oncologists at Strong Memorial Hospital, Highland Hospital, The Genesee Hospital, Rocheste r G eneral H ospital, G eneva G eneral and St. M ary s Hospital for referring patient samples for study and for allowing us access to th eir p atien t s medical records. Thanks are extended to Carol Cole for clerical and secretarial assistance. References 1. B l u m b e r g, N., M a s e l, D. and St o l e r, M.: Disparities in estimates of IgG bound to normal platelets. Blood 67: C in e s, D. B., W il s o n, S. B., T o m a sk i, A. and Sc h r e ib e r, A. D.: Platelet antibodies of the IgM class in im m une throm bocytopenic p u r pura. J. Clin. Invest. 75: , C o u r t, W., B o z e m a n, J. M., So o n g, S.-j., Sa l e h, M. N., Sh a w, D. R. a n d L o B u g l io, A. F.: P la te le t s u rfa c e -b o u n d IgG in p a tie n ts w ith im m u n e a n d n o n im m u n e th ro m b o c y to penias. Blood 69: , H e g d e, U. M., Bo w e s, A. and Ro t e r, B. L. T.: P latelet associated com plem ent com ponents (PAC^ and PAC3d in patients with autoimmune thrombocytopenia. Brit. J. Haematol. 60:49-55, H e l m e r h o r s t, F. M., van L e e u w e n, E. F., P e g e l s, J. G., van d e r P l a s-van D a l e n, C., E n g e l f r i e t, C. P., an d v o n d e m B o r n e, A. E. G. Kr. : Primary and secondary autoimm une throm bocytopenia. Scan. J. Haematol. 28: , K a r p a t k i n, S.: Autoimmune thrombocytopenic purpura. Semin. Hematol. 22: , K a y s e r, W., M u e l l e r - E c k h a r d t, C. and M u e l l e r -E c k h a r d t, G.: The value of plateletassociated IgG in predicting the efficacy of splenectom y in autoim m une throm bocytopenia. Scand. J. Haematol. 30:30 35, K e l t o n, J. G., C a r t e r, C. J., R o d g e r, C., B e b e n e k, G, G a u l d ie, J., S h e r id a n, D., K assa m, Y. B., K e a n, W. F., B u c h a n a n, W. W., R o o n e y, P. J., Bia n c h i, F. and D e n b u r g, J.: The relationship among platelet-associated IgG, platelet lifespan, and reticuloendothelial cell function. Blood 63: , K e l t o n, J. G. and G ib b o n s, S.: Autoimmune platelet destruction: Idiopathic throm bocytop e n ic p u rp u ra. Sem in. T h ro m b. H em ost. 8:83-104, K e l t o n, J. G., P o w e r s, P. J. and C a r ter, C. J.: A prospective study of the usefulness of the measurement of platelet-associated IgG for the diagnosis of idiopathic thrombocytopenic purpura. Blood 60: , Ke r n o ff, L. M. and Malan, E.: P latelet antib o d y le v e ls d o n o t c o rre la te w ith re s p o n se to th e ra p y in id io p a th ic th ro m b o c y to p e n ic p u r p u ra. B rit.j. H aem ato l. 5 3 : , 1983.

10 12. M c F a r l a n d, J., L e t e l l ie r, S., G o t t s c h a l l, J., An d er so n, J. and Aster, R. H.: Measurem ent of total platelet-associated IgG and IgM (PAIgG, PAIgM ) in immune thrombocytopenia. Blood 66:293a, M y er s, T. J., Kim, B. K., St e in e r, M. and B ald in i, M. G. : Platelet-associated complement C3 in im m une throm bocytopenic purpura. Blood 59: , N e l, J. D., St e v e n s, K., M o u t o n, A. and Pretorius, F. J. : Platelet-bound IgM in autoimmune thrombocytopenia. Blood 6J: , Pa n z e r, S., S z a m a i, S., BÖd e k e r, R. - H., H aas, O. A., H a u b e n s t o c k, A. and M u e l l e r - E c k h a r d t, C.: Platelet-associated immunoglobulins IgG, IgM, IgA and com plem ent C3 in CLINICAL ASPECTS OF ELEVATED PAIgG/IgM 33 im mune and non-im mune thrombocytopenic disorders. Amer. J. Hemat. 23:89-99, Pa w h a, J., G iu l ia n i, D., and M orse, B. S.: Platelet-associated IgM levels in thrombocytopenia. Vox Sanguinis 45:97-103, Spitalnik, S.; C o w les, J.; C ox, M. T., Baker, D., H o l t, J., B l u m b e r g, N.: A new technique in quantitative immunohematology: Solid-phase kinetic enzym e-linked im m unosorbent assay. Vox Sang. 45: , van L e e u w e n, E. F., von d e m B o r n e, A. E. G. K r, van d e r P las-van D a l e n, C. and E n g e l - FRIET, C. P. : Idiopathic thrombocytopenic purpura in children; detection of platelet autoantibodies by im m u nofluorescence. Scand. J. Haematol. 26: , 1981.