P2 Microglobulin: Its Significance and Clinical Usefulness

Transcription

1 ANNALS O F CLIN ICAL AND LABORATORY SC IEN CE, Vol. 20, No. 3 Copyright 1990, Institute for Clinical Science, Inc. P2 Microglobulin: Its Significance and Clinical Usefulness MARC BETHEA, M.D. and DONALD T. FORMAN, Ph.D. Division of Clinical Chemistry, North Carolina Memorial Hospital, University of North Carolina, Chapel Hill, NC ABSTRACT P2-Microglobulin (P2M), an interesting and underutilized metabolite, can be used in assessing renal function, particularly in kidney-transplant recipients and in patients suspected of having renal tubulointerstitial disease. It also can serve as a nonspecific but relatively sensitive marker of various neoplastic, inflammatory, and infectious conditions. Early hopes that it would be a useful serum test for malignancy have not been fulfilled, but it does have prognostic value for patients with lymphoproliferative disease, particularly m ultiple myeloma. More recent reports have suggested a role for (J2M as a prognostic m arker in human immunodeficiency virus (HIV) infection. Introduction Since its isolation in 1964 from the urine of patients with W ilson s disease and workers exposed to cadmium, 32- Microglobulin ( 32M) has elicited interest both as an indicator of renal function and as a relatively sensitive though nonspecific m ark e r of c e rta in m alig n an cies, autoim m une diseases, and viral infections, m ost recently acquired im m unodeficiency syndrom e (AIDS). An overview is provided of the current status of f$2m assay with particular emphasis on its role in the m anagem ent of lympho- * Send reprint requests to Donald T. Forman, Ph.D., Division of Clinical Chemistry, 1067 Patient Support Tower, North Carolina Memorial Hospital, University of North Carolina, Chapel Hill, NC proliferative disease and its prognostic value in HIV infection. P2-Microglobulin has been identified as th e lig h t c h a in com m on to th e HLA-A, -B, and -C m ajor histocom patibility complex antigens, and, as such, is expressed on the surface of virtually all norm al n u cleated cells as w ell as by many tum or cell lines. A low concentration of free p2m, about 0.9 to 2.5 mg per L, is found in the serum of healthy subjects, apparently reflecting its shedding from the cell m em brane as a consequence of the turnover of HLA.26 The surfaces of lymphocytes and monocytes are particularly rich in (32M, and lym phocytic synthesis and expression are further augm ented by stimulation with mitogens or with interferons.2 Although the function of surface P2M rem ains /90/ $00.90 Institute for Clinical Science, Inc.

2 1 64 BETHEA AND FORMAN obscure, increased concentrations of (32M in serum have been consistently observed in conditions characterized by lym phocyte activation and (or) proliferation. (32-M icroglobulin may therefore serve as a useful nonspecific marker, in the absence of renal insufficiency, of systemic lymphocytic activation. In table I are d escrib ed various im m unological properties of 32M. In these settings, high serum (32M values can be thought of as a result of increased synthesis w hether owing to increased expression, increased HLA turnover, cell proliferation, cell lysis, or some combination of these - and not of decreased renal clearance.14 Significance of in Renal D isorders The unique features of the renal handling of 02M have prom pted investigation into its role in evaluation of renal function, p articu larly in kidney tra n s plant recip ien ts and in patients susp ected of having tubulointerstitial disease.24 By virtue of its low m olecular mass (11800 Da), (32M is easily filtered through the glomerular basem ent m em brane. Its rapid elim ination is accomplished almost exclusively by glomerular T A B L E I Immunologic Characterization of Beta-2-MicroglobuIin (82 M) 32M is non-covalently associated with histocompatibility antigens. B2m may control the expression of antigens on the cell surface and possibly their biosynthesis. B2M has an amino acid homology and structural similarity to the CH3 region of IgG. S2M is antigenically distinct from IgG. 82M does not bind to antibody-coated protein A-bearing Staphylococcus aureus. $2M appears to inhibit phytohemagglutinin (PHA) induced lymphocyte transformation. Mitogen-induced lymphocyte stimulation in vitro results in marked increase of 02M production. filtration. O f the filtered 32M, 99.9 p ercent is then taken up by endocytosis into proximal tubular cells and catabolized into its constituent amino acids. Serum (32M determinations have been used to follow changes in glom erular filtration rate (GFR); urinary excretion above the normal maximum of approximately 370 jxg p e r 24 hours is taken to indicate tubular dysfunction. Both of these variables have been utilized in the management of renal-transplant patients, a setting in which rapid changes in GFR may be seen.13 In the presence of acute rejection, serum (32M c o n cen tratio n s typically becom e in creased days before serum creatinine increases; fu rth e rm o re, seru m p2m values are independent of body mass or sex. A stable serum (32M in the face of postsurgical oliguria m ay h e lp d istin guish acute renal failure from rejection, and its increased urinary excretion may signify cyclosporin A toxicity.22 The use of 02M determ inations m ust take into account their nonspecificity; however, because an increased serum (32M in this setting may be seen in system ic cytomegalovirus infection, it could prom pt inappropriate high-dose steroid therapy if used as the sole criterion of rejection.3 P2-Microglobulin has also been determ ined in urine as an early indicator of am inoglycoside or lithium toxicity; to screen for heavy m etal (cadmium, m ercury) poisoning in appropriate populations; to help differentiate infections of the upper urinary tract from those of the lower urinary tract; and as an adjunct in th e diagnosis of acute tubular necrosis.24 Significance of (i2m in N eoplasia An association betw een increased (32M in serum and the presence of malignancy was n o ted by several observers soon after the p rotein was characterized, prom pting a flurry of reports concerning its possible use as a tum or m arker (fig

3 CLINICAL USEFULNESS OF pr MICROGLOBULIN /3-CELL NEOPLASIA Plasms Cell Tumors Non-Hodgkins Lymphoma CHR Lymphocytic Leukemia 83 i 8 9 I 5 j j Multiple Myeloma O i Lymphosarcoma 27 M «Reticulum Cell Sarcoma OTHER 11 Solid Tumors* 77???S* Monocytic Leukemia Hodgkins Disease Infectious Mononucleosis Viral Hepatitis Chronic Active Hepatitis Primary Biliary Cirrhosis 5 «13 15 M IM m, 7 1 M iiss \ I I " 1 " 0 < Serum /32-rnicroglobulin (mg/l) F i g u r e 1. Concentration of serum P2M in various B -cell n eopla sia s, solid m alignancies, m iscellaneous malignancies, and various benign infectious disorders. Gray stippled area on figure represents a number of subjects w ith in th e r e f e r e n c e interval (0.9 to 3.0 mg per 1) in the population studied.14 ^includes head, neck, hepatoma, colon, pancreas, stomach, lung, breast, and cervix ure I).14,25 p2-m icroglobulin has since fallen prey to th e difficulties encountered with other serum tests for cancer: disappearance of predictive power when applied to unselected populations, unacceptably low specificity, and the like.23 It has retained some favor as an adjunct in the staging of m ultiple myeloma (MM) and to a lesser degree in B-cell chronic lym phocytic leukem ia (B-CLL), how ever, and may be of use in selected cases in other lym phoproliferative disorders.19 Bataille e t al.4 correlated pre-treatm ent serum (32M values for 115 MM patients with other prognostic features and with subsequent course. They found serum (32M to have powerful predictive value independent of the effect of diminish e d c re a tin in e c le a ra n c e. T hose patients with pre-treatm ent values <six mg per L had a dramatically longer survival tim e (m edian, 52 m onths) than th o se w ith v a lu e s > s ix m g p e r L (m ed ian, 26 m o n th s). S u b s e q u e n t reports, with one exception,28 confirm the predictive power of serum (32M assay and note significant correlation w ith stage and tum or cell mass.1 Garewal et al.16 found that, in some patients, serum (32M appeared to correlate b etter with observed response to treatm ent than did changes in the concentration of the M- component. Serum (32M values m ust be interpreted with caution in MM; however, although a statistically significant difference can be dem onstrated between (32M values in patients w ith benign monoclonal gammopathies and patients w ith stage I m yelom a, there is a not inconsiderable overlap betw een the two

4 1 66 BETHEA AND FORMAN groups.19 M ore importantly, there is a subset of patients with MM (eight of 90 in a 1987 prospective study5) who never show an increase in serum (32M. The value of d e te rm in in g 32M in patients w ith B-CLL is less well-established. Melillo e t al19 showed a consistent increase in pre-treatm ent values for a group of 34 patients, as well as significant correlation with clinical stage (Stage I vs III or IV, Stage II vs III or IV; P < 0.05) a n d a sig n ific a n t (P < 0.01) decrease in values for patients responsive to therapy. However, the study confirmed earlier reports of a wide overlap b e tw e e n p re -tre a tm e n t values and values in responders and also failed to show a return to normal concentrations in any patient. The latter likely reflects a true phenom enon, because complete eradication of the neoplastic clone in CLL is rare. Ellegaard et al11 concluded that rep eated 2M determ inations in serum may be of value in estimating the residual tum or mass after therapy, a conclusion shared by other investigators.19 Several studies have a tte m p te d to define a role for (32M assay in the managem ent of non-h odgkin s lym phom a (NHL) or in H odgkin s disease (HD). A lthough statistical correlations w ith stage at diagnosis and histological grade have been shown, the wide dispersion of values lim its the usefulness of serum (32M as a m arker of disease activity.19 In additio n, H D p a tie n ts in fre q u en tly exhibit a significantly increased serum (32M unless they have w idespread disease. M easurem ents of (32M in cerebrospinal fluid (CSF) may have value in detecting the presence of lymphoma or leukemia in the central nervous system, although rep e a t tests for recu rren ce m u st tak e in to acco u n t n o n sp ecific increases in CSF-fS2M owing to intrathecal chem otherapy.21 Significantly in creased values for seru m a re n o t lim ite d to ly m p h o id malignancies and have been observed in some solid tum ors as well (figure 1). The clinical utility of this observation is questionable, however. Lotzniker et al18 published a surprising result based on a study of 186 carcinoma patients. Those with stage IV disease had significantly low er serum (32M values than those in stages II or III (P < 0.01). Immunohistological studies with use of antibodies to surface (32M have shown a tendency for decreased expression in m ore poorly differentiated carcinomas Lotzniker et al18 speculated that serum 32M may serve as an interesting m arker of differentiation rather than a tum or marker per se; decreased serum (32M might directly reflect less tum or cell HLA turnover or m ay in d ic a te an im p a ire d im m u n e resp o n se d u e to a lte re d reco g n itio n sites. Significance of Serum p2m in Chronic Inflammatory Conditions and in AIDS Serum 32M values are increased in some chronic inflammatory or possibly autoim m une conditions, including systemic lupus erythematosus, rheum atoid a rth ritis, S jo g re n s sy n d ro m e, and C r o h n s d is e a s e, am o n g o t h e r s.14 Reviews of the utility of (32M as a monitor of disease activity have been mixed. Dixon et al10 pointed out the difficulty of assessin g th e c o n trib u tio n o f ren a l im pairm ent to an increased value for (32M in serum, particularly in patients who may have subclinical glom erular and tubular dysfunction resulting from chronic non-steroidal anti-inflammatory drug use. p2-m icroglobulin has been m easured in synovial fluid and saliva in rheum atoid arthritis and Sjogren s syndrom e, respectively, and suggested as indices of lymphocyte turnover. A 32M response has been shown in certain viral infections, including infectious m ononucleosis, cytom egalovirus,

5 CLINICAL USEFULNESS OF P,-MICROGLOBULIN non-a non-b hepatitis,8 and AIDS.15 The nonspecificity and variab ility of the response render it of little value for diagnostic purposes, although a high value in an im m unosuppressed p atie n t m ight prom pt the clinician to consider the possibility of opportunistic viral infection.8 (32-Microglobulin may also play a role in evaluating prognosis and m onitoring tre a tm e n t in H IV -in fected p a tie n ts. Bhalla et al6 reported above-normal concentrations in 29 of 31 AIDS patients as well as five of 11 asymptomatic homosexual m en. Zoila-Pazner et al30 prospectively studied 40 asym ptom atic hom o sexual m en from New York City, whose cases were followed for two years. Six of th e seven subjects w ith initial serum value > 2.5 mg per L developed AIDS, whereas none of the remaining subjects p ro g re ssed to A ID S d u rin g th e two years. Recent reports at the Fourth and F ifth In tern atio n al C onference(s) on AIDS (Stockholm, June 1988 and M ontreal, June 1989) continue to substantiate that serum (32M is a useful surrogate test for predicting the developm ent of AIDS. One paper, based on a prospective study of 215 H IV -antibody-positive subjects whose cases were followed for a median period of 30 months, suggested a multivariate m odel for predicting AIDS by T A B L E II Use of Serum Beta-2-Microglobulin, Urinary Neopterin and T-Cell Subsets in Predicting the Progression of HIV Disease in Hemophiliacs Test Result Relative Risk of Developing CDC Group IV Disease in Four Years CD-4 < (p = 0.07) 82M >3.0 mg/l 10 (p = 0.02) Neopterin > 15 nmol/l 6 (p = 0.11) (3.8 ng/l) Cuthbert, R.J.G.: Combination of beta-2-microglobuin, neopterin and T-cell subsets is useful in predicting the progression of HIV disease in hemophiliacs. Poster T.B.P. 74, Fifth International Conference on AIDS, Montreal, Canada, June 6, use of serum p2m determinations, C positive lym phocyte counts, and m easurem ents of anti-p24 and p24 antigen.20 In table II is shown the relative risk of d ev elo p in g C D C G roup IV disease. A nother presentation suggested that a decrease or normalization of serum (32M during the first eight to 12 weeks of azathioprine (AZT) therapy was predictive of a stable clinical status for 14 to 18 m onths.17 An additional report showed a strongly positive correlation betw een clinical severity of AIDS-dementia complex and p2m concentrations in the cerebrospinal flu id.7 M easurem ent of (J2M T here are several reliable m ethods quantifying pi2m, including laser nephelo m e try,9 rad io im m u n o assay,27 and enzyme immunoassay.12 The last two are the more sensitive and widely used techniques. These two m ethods allow detection of trace amounts of P2M in normal serum and urine and effectively distinguish norm al from high concentrations. 32-M icroglobulin is stable in serum, and samples can be stored at 20 C for as long as a year. U rinary assays are problem atic, however, because (32M is rapidly degraded at phs <6.0. Although some investigators simply add alkali to the specimen, Schardijn24 recommends giving the subject four g of sodium bicarbonate on the evening before collection and an additional divided dose of four g during the 24 hour period to obviate degradation w ithin the bladder. References 1. A l e x a n i a n, R., B a t l o g i e, B. and F r i t s c h e, H.: Betaa-microglobulin in multiple myeloma. Am. J. Hematol. 20: , Azocar, J., E ssex, M., Watson, A., G a zit, E., An d e r s o n, D., and Yu n is, E.: Changes in the expression of HLA and p2 microgl bulin by cultured lymphoid cells. Human Immunol. 5: , 1982.

6 168 BETHEA AND FORMAN 3. Backman, L., Ringden, D., Bjôrkhen, I., and LlNDBACK, B.: Increased serum p2-microglobulin during rejection, cyclosporine induced nephrotoxicity, and cytomegalovirus infection in renal transplant recipients. Transplantation 42: , B a t a i l l e, R., D u r i e, B., and G r e n i e r, J. : Serum P2-microglobulin and survival duration in multiple myeloma: a simple reliable marker for staging. Brit. J. Haematol. 55: , B a t a il l e, R., G r e n ie r, J., and S u n y, J.: Unexp ected norm al serum beta-2-m icroglobulin levels in m ultiple myeloma. Anticancer Res. 7: , B h a l l a, R., S a f a i, B., M e r t e l s m a n n, R., and S c h w a r t z, M.: Abnormally high concentrations of fj2-microglobulin in acquired immunodeficiency syndrome (AIDS) patients. Clin. Chem. 29:1560, Br e w, B. J.: CSF beta-2-microglobulin is a sensitive but non-specific marker for AIDS dementia. Poster T.B.P. 233, Fifth International Conf on AIDS. Montreal, Canada, June C o o p e r, E., F o r b e s, M., and H a m m b l i n g, M.: Serum 32-microglobulin and C-reactive protein concentrations in viral infections. J. Clin. Path. 37: , D e s j a r l a is, F., and D a i g n e a u l t, R.: Limitations of conventional laser nephelometry for the measurement of p2-microglobuiin, lysozyme, a J- fetoprotein and myoglobin in serum and urine. Clin. Biochem. 74: , D i x o n, J., B o j a r, R., and S a u n d e r s, N.: I s measurement of 32-microglobulin worthwhile? Brit. J. Rheumatol. 27:80-81, E l l e g a a r d, J., M o g e n s e n, C., and K r a g - BALLE, K. : Serum (}2-microglobulin levels in acute and chronic leukemia. Scand. J. Hematol. 25: , F e r r u a, B., V i n c e n t, C., R e v i l ia r d, J. P., et al: A sandwich method of enzyme immunoassay. III. Assay for human beta-2-microglobulin compared w ith radioimmunoassay. J. Immunol. Methods. 36: , F i n n, W., H u f f m a n, K., F o r m a n, D., and M a n d e l, S. : Value of the serum f$2-microglobulin serum creatinine ratio following renal transplantation. Transplant. Proc. i6 : , F o r m a n, D.: Serum P2-m icroglobulin as an indicator of neoplasia. J. Clin. Immunoassay 6: , F r a n c i o l i, P. and C l e m e n t, F. : Beta^microglobulin and immunodeficiency in a homosexual man. New Engl. J. Med. 307: , G a r e w a l, H., D u r i e, B., K y l e, R., F in l e y, P., B o w e r, B., and S e r o k m a n, R.: Serum (32- microglobulin in the initial staging and subsequent monitoring of monoclonal plasma cell disorder. J. Clin. Oncol. 2:51-57, Ja c o b s o n, M. A., K r a m p f, W., C h a i s s o n, R. E., and O s m o n d, D.: Changes in serum beta-2-microglobulin level predicts clinical outcome during AZT therapy. Poster T.B.P. 312, Fifth International Conf on AIDS, Montreal, Canada, June L o t z n ik e r, M., Pa v e s i, F., M a r b e l l o, L., M o r a t ti, R., et al: Beta-2-microglobulin as a tumor marker in solid malignancies. Oncology 45: , M e l il l o, L., M u st o, P., T o m a s i, P., e t al: Serum (32_micr0Sl t,lilin in malignant lymphoproliferative disease. Tumor 74: , Moss, A. R., Ba c c h e t t i, P., O s m o n d, D., etal: Seropositivity for HIV and the development of AIDS or AIDS related condition: three year follow-up of the San Francisco General Hospital cohort. Brit. Med. J. 296: , M u st o, P., T o m a si, P., C ascavilla, N., et al: Significance and limits of cerebrospinal fluid beta-2-microglobulin measurement in course of acute lymphoblastic leukemia. Am. J. Hematol. 28: , P r is c h l, F, G r e m m e l, F., Sc h w a b e, M., etal: Beta-2-microglobulin for differentiation between cyclosporin A nephrotoxicity and graft rejection in renal transplant recipient. Nephron 5i: , P o u l ik, M., P erry, D., an d Se k in e, T.: S tatistical analysis o f i2-m icroglobulin levels in se ra of lu n g a n d G I tra c t c a n c e r p a tie n ts. Vox Sang. 38: , SCHARDIJN, G. and VAN Eps, L.: 02-microglobulin: its significance in the evaluation of renal function. Kidney Internat. 32: , S h u st e r, J., G o l d, P., and P o u l ik, M.: 0 2- microglobulin levels in cancerous and other disease states. Clin. Chim. Acta 42: , Sidky, K. and Walker, R.: (32-microglobulin in nonmalignant and malignant human breast: a feature of differentiation. J. Path. 142: , Sw a n so n, R. A., T racy, R. P., Katzm an, J. A., W il s o n, D., and Yo u n g, D.: {J2-Microglobulin determined by radioimmunoassay with monoclonal antibody. Clin. Chem. 28: , van D o b b e n b u r g h, O., Ro d e n h u is, S., O u k- HUIZEN, T., et al: Serum beta-2-microglobulin: a real improvement in the management of multiple myeloma? Brit. J. Haematol. 61: , W a l t o n, G., M c C u e, P., and G r a h a m, S.: B eta-2-m icroglobulins as a differentiation marker in bladder cancer. J. Urol. /o6: , Z o lla-pa zner, S., W il l ia m, D., E l S adr, W., Marm o r, M., and St a h l, R.: Quantitation of P2-microglobulin and other immune characteristics in a prospective study of men at risk for AIDS. J. Am. Med. Assoc. 251: , 1984.