- Ensherah Mokheemer. - Rama Nada. - Tareq Aladily. 1 P a g e

Transcription

1 -3 - Ensherah Mokheemer - Rama Nada - Tareq Aladily 1 P a g e

2 In this lecture we will continue talking about autoimmune hemolytic anemia. Autoimmune hemolytic anemia - There are several types that shares the same phenomena which is the presence of an immunoglobulin attached to their RBCs surface which causes destruction later on by macrophages in the spleen. A group of anaemias in which an abnormal immunoglobulin is attached to RBC membrane. - Coombs Test it is a test done in the hospital to detect the presence of the antibodies coating the RBCs, we have two tests the direct and indirect, The direct Coombs test is used to test for autoimmune hemolytic anemia, we give antibodies that binds to the immunoglobulin (autoantibody) on the RBC membrane, this binding leads to agglutination** of the RBC, we can also give RBCS which will bind the autoantibodies -if they are present- and cause agglutination. Coombs test: the patient's blood is mixed with serum containing antibodies that are specific for human immunoglobulin. If the autoantibody is present, agglutination of RBC occurs. ** Agglutination means large aggregates of RBCs that becomes clump to each other and the become viscous and turbid. - We have two types of autoimmune hemolytic anemia we classify them based on their site of activity in the blood : 1) Warm Antibody Type: usually occurs in the trunk of our bodies where the temperature is 37. 2) Cold antibody type: which occurs in the periphery of the body (Fingers, nose, ears) where the temperature is below 37. Now let s talk about them in detail: 1) Warm antibody Type: - Most common 70% of the cases. - 50% are idiopathic (primary) there is no obvious cause; the others are related to either exposure to a drug (mostly penicillin and cephalosporins) which is more common, or they have other autoimmune diseases such as systemic lupus erythematosus. - Most causative antibodies are of the IgG class; less commonly, IgA antibodies 2 P a g e

3 - A common target is the Rh antigen on RBCs. - These abnormal Antibodies (autoantibodies) that coat the RBCs, have receptors on the macrophages so when they go to the spleen they will bind to the fc receptor on the phagocytes, the phagocytes will remove the part of the RBC membrane which antibodies are bound to ( it pinches that part of the membrane), this process is called partial phagocytosis because we lose small fragments of the RBC membrane not the whole RBC is lost. With the continuous loss of fragments, the RBCs will become smaller and rounder (spherocytes/ ball like). In the secondary circulation when they go back to the spleen, they will be destroyed due to their abnormal shape. The red cell haemolysis is mostly extravascular. IgG-coated red cells bind to Fc receptors on phagocytes, which remove red cell membrane during "partial" phagocytosis. As in hereditary spherocytosis, the loss of membrane converts the red cells to spherocytes, which are removed in the spleen. - Moderate splenomegaly and extravascular haemolytic anaemia. Drug induced hemolytic anemia: A) Antigenic drugs: when certain drugs (especially antibiotics and antimalarial drugs) are given at high dose (intravenous) these drugs bind to the cell membrane of the RBC they act as a hapten small molecule that binds to another molecule attracting antibodies eventually the body will recognise them as antigens and produce IgG antibodies against them. - The haemolytic anaemia occurs in 1 to 2 weeks after therapy is initiated that is because the synthesis of antibodies IgG takes time. - Example of these drugs are: Penicillin, cephalosporin, anti-malaria drugs. - Antigenic drugs mean that the drug works as an antigen. B) Tolerance-breaking drugs -Unknown mechanism but there is no binding of the drug to the RBC -Activates production of autoantibodies against Rh group -α-methyldopa: anti-hypertensive drug commonly used in pregnancy 3 P a g e

4 Note: the first type the antigenic drugs is not a true autoimmune disease because the antibodies were not produced against selfantigens directly, they were produced against drugs (not selfantigens) but they attacked the self-antigen RH that s why we put them along with autoimmune diseases (but they are not true autoimmune diseases). As for the second type tolerance breaking drugs it is a true autoimmune disease because the antibodies were directly produced against self-antigens (Rh antigen). 2) Cold Agglutinin Type: - IgM antibodies (IgM is the largest antibody is pentamer (5 binding sites)) - IgM bind red cells at low temperatures, but the binding is weak when it reaches the trunk of the body where the temperature is high it dissociates. But when it is bound to the RBC in the periphery it attracts small amounts of the complement system (C3b), which is recognized by macrophages in the spleen and removed the same mechanism as the warm type first we have spherocytes then they are removed by the spleen.. - IgM is functioning the best at low temperatures (0-4 c) and it is seen in the nose, fingers, ears. - less common than warm immunohymolytic anaemia: Acute: Self-limited, following infection by Mycoplasma pneumonia (Atypical anemia), Epstein-Barr virus, cytomegalovirus, influenza virus, and HIV. Chronic: associated with B- cell lymphoma, severe. Why does it occur in lymphoma? In B-cell lymphoma there are large numbers of B lymphocytes and they are not normal which increases the risk of formation of auto-antibodies. 4 P a g e

5 - Under the microscope we see RBC agglutination in autoimmune haemolytic anaemia only in cold AIHA. Because IgM is a pentamer an it can bind to many RBCs. In IgG in the warm AIHA we don t see agglutination we only see spherocytes. Haemolytic Anaemia Resulting from Trauma to Red Cells - This type of anaemia is secondary to mechanical damage to t RBCs - Physical damage to RBCs: (1) Cardiac valve prosthesis (we replace the soft tissue with metal which will injure the RBCs). (2) Vigorous exercise, but it s mostly not significant (that s mean if you see schistocytes in the blood film for an athlete it doesn t mean medically significant anemia), its rarely seen. (3) Microangiopathic diseases (diseases in the small vessels) the most important category: (a)disseminated intravascular coagulation (DIC) (b)thrombotic thrombocytopenic purpura (TTP) (c)hemolytic-uremic syndrome (HUS), aggregates of fibrin and platelets causes damage to RBCs **These three diseases share wide spread thrombosis in the small blood vessels. 5 P a g e

6 - RBCs appear as fragments (schistocytes). torn RBCs. - Now we will star talking about hemoglobinopathies, disorders which are related to abnormal haemoglobin synthesis. Thalassemia - Heterogeneous group (not a single disease) of disorders caused by inherited mutations that decrease the synthesis of adult hemoglobin, HgA (α2β2). - Autosomal Recessive. - We classify it according to the severity and the type of the chain that is deficient (α or β). - Endemic (always persistent in large number) in Middle East, tropical Africa, India, Asia (not common in Europe). - β-thalassemia is caused by deficient synthesis of β chains, whereas α-thalassemia is caused by deficient synthesis of α chains. - The consequence of the diminished synthesis of one globin chain leads to the relative excess in the other globin chain and this excess causes harm to the RBC, leading to their haemolysis. - Hence that in thalassemia the bone marrow is producing RBCs but they are deficient (empty) and this is by definition called anaemia because it is a decrease in the RBC mass not in their number. - The hematologic consequences of diminished synthesis of one globin chain stem not only from hemoglobin deficiency but also 6 P a g e

7 from a relative excess of the other globin chain, particularly in β- thalassemia. β-thalassemia: - caused by mutations that diminish the synthesis of β-globin chains (chromosome 11). - There are two types of mutations which differ in their severity: 1- β0 mutations, associated with absent β-globin synthesis. Remember that we have two alleles one is maternal, and the other is paternal so of there is a β0 mutation in one of them and the other is normal the patient survives. 2- β+ mutations, characterized by reduced (but detectable) β- globin synthesis. In this case it is either a decrease in the globin synthesis or slower rate of production different causative mutations, mostly consisting of point mutations, the severity of anemia vary according to the mutation. - Pathogenesis: Lower production of HgA so the RBCs will appear hypochromic, microcytic and the patient will suffer from hypoxia. β-thalassemia does not appear early in life, because in newborns we have a higher percentage of foetal haemoglobin, so it masks the deficient of beta chain (remember that HbF is composed of two alpha chains and two gamma chains). At the ag of 6 month the foetal haemoglobin level becomes low and not sufficient to mask the deficiency eventually thalassemia symptoms appear. Unpaired α chains precipitate (insoluble) in erythroid precursors and RBCs, causing membrane damage which leads to haemolysis in BM, blood and spleen. So, it is a haemolytic anaemia. In bone marrow: Due to hypoxia, erythropoietin is released from the kidney activating the bone marrow to produce erythroid cell there is a marked erythroid hyperplasia eroding bone and shifting oxygen and nutrients leading skeletal deformity and growth retardation (this occurs in thalassemia major). 7 P a g e

8 Ineffective erythropoiesis which means we have large number of erythroid precursors but still the anaemia is not corrected because we have a genetic disease in order to compensate the ineffective erythropoiesis the body will activate other sites to produce RBCs and this is called extramedullary haematopoiesis (Haematopoiesis outside bone marrow results from persistent stimulation of erythropoietin, such as in spleen liver and sometime lymph nodes) and this will lead to enlargement of these organs. We treat them by Repeated blood transfusion + Hepcidin will be suppressed as a result of increased erythropoietin these two factors will cause hemosiderosis. In blood transfusion the patients receive RBCs and RBCs have iron inside them, so this will increase the iron in the body. As for hepcidin it is a protein that reduces iron uptake from the intestinal cells so when it is supressed iron uptake will increase leading to increase in the iron level in the body. These two factors contribute to the occurrence of hemosiderosis in patients with thalassemia major. Hemosiderosis means excess amounts of iron, iron will accumulate in the tissues of the body causing physical damage especially to the heart, kidney and endocrine system. - Clinical classification: 1- β -thal minor: loss of one β alleles, asymptomatic it could be β+/β or βo/β. In these patients, RBCs colour and size is below normal, so in the blood film of these patients you will see microcytic, hypochromic anaemia. this is the requested test before marriage. 2- β thal intermedia: mutations in two β alleles. Patients have moderate anaemia, but stable and it could be β+/β+ or βo/β+. These patients do not receive blood transfusion. 3- β thal major: loss of two β alleles. Severe symptoms (βo/βo). α- Thalassemia - It is usually deletion mutations - We have 4 alpha genes. 8 P a g e

9 - In case of α thalassemia there is excess of β chains and γ chains. - Since free β and γ chains are more soluble than free α chains, haemolysis and ineffective erythropoiesis are less severe than in β-thalassemia. - As in β-thalassemia, the anaemia occurs both from inadequate haemoglobin synthesis and the effects of excess unpaired non-α chains (β, γ, and δ). - Tetra gamma haemoglobin it is called haemoglobin Bart, tetra β is called haemoglobin H. we use these two in diagnosis of α thalassemia. In newborns with α-thalassemia, excess unpaired γ-globin chains form γ4 tetramers known as hemoglobin Barts, whereas in older children and adults excess β-globin chains form β4 tetramers known as HgH, resembles β- intermedia. - Clinical classification: remember we have 4 α genes: Silent carrier: a single gene deletion, patients have slight microcytosis but no anemia, asymptomatic. α-thalassemia Trait: deletion of two genes, but still we have two functional genes. Clinically identical to β-thalassemia minor: microcytosis, minimal or no anemia, aymptomatic Hemoglobin H Disease: deletion of 3 alpha genes, common in Asia, clinically resembles β-thalassemia intermedia. In this type we have excess beta and gamma chains. Hydrops fetalis: deletion of 4 alpha genes. Patients die in utero, that is because alpha chains are present in foetal haemoglobin in addition to adult haemoglobin. The babies are incompatible for life unless they are transfused, and this is not accessible in most patients. - Diagnosis of thalassemia: 1- Blood film: hypochromic microcytic anaemia, target cells**, basophilic stippling*. **Target cells: the RBC appear dark in periphery then pale in the centre and then dark again this appearance is not specific for thalassemia, it is for all the diseases in which there is abnormal haemoglobin synthesis (Iron deficiency and sickle cell anemia), so it s not specific for thalassemia. 9 P a g e

10 Target cells Basophilic stippling *Basophilic stippling: small basophilic dots everywhere in RBCs, they are aggregates of ribosomes, appear as fine blue inclusions in RBCs. 2- Hg electrophoresis: different globin chains have different electrical charges. Hg is separated on gel and an electrical current is applied. Each type of Hg migrates a specific distance and hence can be recognized, the globin with low concentration will appear as small band (in case of beta thalassemia, HbA will give small band and HbA2 will give band larger than normal). This test gives us the definite diagnosis. 3-In β-thalassemia, HgA2 in increased because it does not have beta chains only alpha and delta and they both increase in beta thalassemia. 4- Genetic test: this is the most accurate and definite test as it tests the type of mutation. Sickle cell anaemia. - autosomal recessive. - Common in Africa, Middle East. - Point mutation (substitution mutation) on β gene, glutamate(hydrophilic) residue is replaced with valine(hydrophobic) (HgS). So, the end result is change in the characteristic of beta chain. - Mutation in one gene: sickle cell trait (silent carrier), HgS =40%, HgA=40% and the remaining 10% is HgA2 and HbF. 10 P a g e

11 - Mutation in 2 genes: sickle cell disease, HgS =90%, we don t have HgA. - Both conditions protect against Malaria falciparum infection. - Pathogenesis: HgS is less soluble so it tends to polymerize longitudinally upon hypoxia, acidity, dehydration these factors lead to decrease in the affinity of haemoglobin toward oxygen, so oxygen is released, and we have more deoxygenated Hb which is polymerised. Needle-like shape Membrane damage Intravascular haemolysis occurs due to membrane damage and extravascular haemolysis occurs when the sickle shaped RBCs are homolysed due to their abnormal shape. Sickled RBCs can bind each other and form a thrombus which will cause Capillary occlusion and ischemic infarction. HgA, HgF prevent sickling, that s why carries do not develop symptoms because they still have HbA which prevents polymerization. Also, symptoms do not appear until the age of 6 months because of HbF prevents polymerization in the first six months. Remember that in thalassemia and sickle cell anaemia symptoms appear at the age of six months and not immediately after birth. With chronic haemolysis: BM, bone changes & extramedullary haematopoiesis similar to thalassemia major. Splenic changes: 1- Early disease: splenomegaly due to extravascular haemolysis. 2- Sequestration crisis: massive entrapment of RBC in spleen, leading to hypovolemia and shock, the spleen becomes engorged with blood until it affects the whole 11 P a g e

12 circulation. The patients will show hypovolemic symptoms and extravascular bleeding. 3- Advanced disease: splenic infarction (autosplenectomy). Because sickle cells form thrombi leading to splenic infarction and atrophy. Vaso-occlusive crisis: Aplastic crisis: Thrombosis, tissue infarction, can be developed in any organ. Bone and joint pain due to multiple bone infarction. Skin ulcer (leg) if it was severe it will lead to infection. Myocardial infarction it is lethal, and it occurs at early age. Acute chest syndrome thrombosis in lungs or bones of the rib cage, which will cause severe pain in the chest. Penis (priapism), continuous erection, the drainage of the penis is blocked by thrombi so eventually it will lead to penis infarction. Parvovirus B19 it affects the erythroid progenitors. Destroys erythroid cells. When normal people get infected their body can cope with the virus, so no symptoms appears. But in patients with thalassemia and sickle cell anaemia, the virus becomes stronger and they suffer from long standing chronic anaemia and aplastic crisis (there is no production of erythroid cells in the bone marrow). Patients present with sudden, severe, worsening of the anaemia. we can diagnose it using serology antibodies against the virus or we can take a biopsy from the bone marrow we can see inclusions in the Nuclei of erythroid precursors (viral particles). 12 P a g e

13 Aplastic crisis: pronormoblast shows nuclear inclusions Also complicates thalassemia. - Diagnosis: 1- Blood film: Sickle cells, Howell Jolly bodies (after splenectomy or the atrophy of the spleen), target cells (due to abnormal haemoglobin synthesis and distribution in the RBC). 13 P a g e 2- Haemoglobin electrophoresis. 3- Crew-cut appearance of skull of X ray: shows the shadow of erythroid cells in the BM, secondary to marked erythropoiesis in sickle cell anaemia and B-thalassemia and they have specific facial features (prominent bones) called sickle face. This is due to very active bone marrow but ineffective erythropoiesis, so they cannot compensate anaemia. Also, they have extramedullary haematopoiesis but still can t compensate anaemia. The End, Sorry for any mistake Good luck