Introduction to Medical Immunology - part 7 pps

Page 451 23.4 Which one of the following pharmacological agents should be immediately administered to a patient with suspected anaphylaxis? A. Antihistaminics B. Cholinergic drugs C. Epinephrine D. Methylxanthines E. Sodium cromoglycate 23.5 Which of the following is coupled to the solid phase in a radioallergosorbent test (RAST) assay? A. A given allergen B. Anti-IgE C. Antibodies to a given allergen D. IgE E. The patient's serum 23.6 Which of the following newly synthesized mast-cell mediators is responsible for the attraction of eosinophils to the peribronchial tissues in the late stages of an asthma attack? A. Eosinophil chemotactic factor-A B. Leukotriene B-4 (LTB-4) C. Major basic protein D. Platelet aggregation factor E. Prostaglandin E2 23.7 Of the following reagents, which one will be able to induce the release of histamine from the mast cells of a ragweed-sensitized individual? A. A univalent fragment of ragweed B. F(ab')2 from an anti-IgE antibody C. Fab from an anti-IgE antibody D. IgE antiragweed E. IgG antiragweed 23.8 A major control mechanism of type I hypersensitivity reactions mediated by eosinophils is the release of: A. Cationic proteins B. Histaminase C. Leukotrienes C4, D4, and E4 D. Major basic protein E. Platelet activating factor 23.9 Which of the following mediators is NOT involved (directly or indirectly) in negative feedback reactions in immediate hypersensitivity? A. Eosinophil chemotactic factor-A B. Histaminase C. Histamine D. Phospholipase D E. Prostaglandin D2 23.10 What is the meaning of the incidental finding of an elevated serum IgE level of 500 IU/mL in a clinically asymptomatic individual? A. The subject is atopic B. HLA-B7 is likely to be represented on the individual's phenotype C. Hyposensitization is not likely to be effective Page 452 D. The individual is a high IgE producer E. The individual is likely to develop allergies Answers 23.1 (B) The Fc ε -RI is the Fc receptor with highest affinity for its ligand (IgE). It is only expressed on basophils and mast cells, which do not mediate ADCC reactions, and is structurally unrelated to the immunoglobulin superfamily. 23.2 (A) Aerosolized glucocorticoids are preferred to systemic glucocorticoids because they are effective in most cases with less risk of development of side effects. Antihistaminics and methylxanthines may have anti-inflammatory properties, but are not sufficiently effective to be useful as primary treatment for chronic asthma. 23.3 (B) Hyposensitization appeared to induce and to increase the activity of antigen-specific suppressor cells that will lead to a decrease in serum IgE levels. 23.4 (C) Epinephrine is the drug of choice for immediate treatment of anaphylaxis. 23.5 (A) The allergen is coupled to the solid phase; if IgE antibodies are present in the patient's serum, they will become bound to the antigen in the solid phase, and their presence can be revealed with a radiolabeled anti-IgE antibody. 23.6 (B) The two other chemotactic factors for eosinophils, platelet activating factor (PAF) and eosinophil chemotactic factor-A (ECF-A), are preformed and released in the early phase. 23.7 (B) The release of histamine requires the cross-linking of membrane IgE which can be induced either by complete anti-IgE antibodies, bivalent F(ab') 2 fragments of anti-IgE antibodies, or multivalent antigen of the right specificity. 23.8 (B) 23.9 (E) Histamine, by reacting with type III histamine receptors in basophils and mast cells, will inhibit further histamine release; phospholipase D degrades PAF; histaminase degrades histamine; LTB-4 is chemotactic for eosinophils, which release phospholipase D, histaminase, and other protective factors. 23.10 (D) Many nonallergic individuals may have IgE values above the upper limit of normalcy. It is not possible to conclude that an individual with high IgE levels is more likely to become allergic. Bibliography Bochner, B.S., Undem, B.J., and Lichtenstein, L.M. Immunological aspects of asthma. Annu. Rev. Immunol., 12: 295, 1994. Bracquet, P., Touqui, L., Shen, T.Y., and Vargaftig, B.B. Perspectives in platelet-activating factor research. Pharmacol. Rev., 39: 97, 1987. Burrows, B., and Lebowitz, M.D. The β -agonist dilemma. N. Engl. J. Med., 326: 560, 1992. Geha, R.S. Regulation of IgE synthesis in humans. J. Allergy Clin. Immunol., 90: 143, 1992. Goetzl, E.J., Payan, D.G., and Goldman, D.W. Immunopathogenetic role of leukotrienes in human diseases. J. Clin. Immunol., 4: 79, 1984. International Consensus Report on Diagnosis and Management of Asthma. U.S. Dept. of Health and Human Services Publication 92–3091, 1992. Postma D., Bleekeer E.R., Amelung P.J., Holroyd, K.J., Jianfeng, X., Panhuysen, C.I.M., Meyers, D., and Levitt, R.C. Genetic susceptibility to asthma-bronchial hyperresponsiveness coinherited with a major gene for atopy. N. Engl. J. Med., 333: 894, 1995. Weller P.F. The immunobiology of eosinophils. N. Engl. J. Med., 324: 1110, 1991. Page 453 24 Immunohematology Gabriel Virella and Mary Ann Spivey I. Introduction: Blood Groups A. The ABO System. The first human red-cell antigen system to be characterized was the ABO blood group system. Specificity is determined by the terminal sugar in an oligosaccharide structure. The terminal sugars of the oligosaccharides defining groups A and B are immunogenic. In group O the precursor H oligosaccharide is unaltered. The red cells express either A, B, both A and B, or neither, and antibodies are found in serum to antigens not expressed by the red cells, as shown in Table 24.1. 1. The ABO group of a given individual is determined by testing both cells and serum. The subject's red cells are mixed with serum containing known antibody, and the subject's serum is tested against cells possessing known antigen. For example, the cells of a group A individual are agglutinated by anti-A serum but not by anti-B serum, and his serum agglutinates type B cells but not type A cells. The typing of cells as group O is done by exclusion (a cell not reacting with anti-A or anti-B is considered to be of blood group O). 2. The anti-A and anti-B isoagglutinins are synthesized as a consequence of cross-immunization with enterobacteriaceae that have outer membrane oligosaccharides strikingly similar to those that define the A and B antigens (see Chap. 13). For example, a newborn with group A blood will not have anti-B in his or her serum, since there has been no opportunity to undergo cross-immunization. When the intestine is eventually colonized by the normal microbial flora, the infant will start to develop anti-B, but will not produce anti-A because of tolerance to his or her own blood group antigens (see Table 24.1). 3. The inheritance of the ABO groups follows simple Mendelian rules; with three common allelic genes: A, B, and O (A can be subdivided into A 1 and A 2 ), of which any individual will carry two, one inherited from the mother, and one from the father. B. The Rh System 1. Historical overview. In 1939, Philip Levine discovered that the sera of most women who gave birth to infants with hemolytic disease contained an antibody that reacted with the red cells of the infant and with the red cells of 85% of Caucasians. In 1940, Landsteiner and Wiener injected blood from the Page 454 Table 24.1 The ABO System Red-cell antigen Serum isoagglutinins Blood group A Anti-B A B Anti-A B A and B None AB None Anti-A and -B O monkey Macacus rhesus into rabbits and guinea pigs and discovered that the resulting antibody agglutinated Rhesus red cells and appeared to have the same specificity as the neonatal antibody. The donors whose cells were agglutinated by the antibody to Rhesus red cells were termed Rh positive; those whose cells were not agglutinated were termed Rh negative. It is now known that the antibody obtained by Landsteiner and Wiener reacts with an antigen (LW) that is different but closely related to the one that is recognized in human hemolytic disease, but the Rh nomenclature was retained. 2. Theories, nomenclatures, and antigens of the Rh system. The Rh system is now known to have many antigens in addition to the one originally described, and several nomenclature systems are in use. a. According to the Fisher-Race theory, the Rh gene complex is formed by combinations of three pairs of allelic genes: Cc, Dd, Ee. The possible combinations are: Dce, DCe, DcE, DCE, dce, dCe, dcE, and dCE. The three closely linked gene loci are inherited as a gene complex. Thus a DCe/DcE individual can only pass DCe or DcE to his offspring and no other combination. The original antigen discovered is called D and people who possess it are called Rh positive. The antigen d has never been discovered, and the symbol “d” is used to denote the absence of D. All individuals lacking the D antigen are termed Rh negative. The most frequent genotype of D-negative individuals is dce/dce. The lack of one Table 24.2 Comparison of the Fisher-Race and Wiener Notations for the Rh System Fisher-Race notation Wiener notation Gene complex Antigens Genes Agglutinogens Factors Dce D,c,e R 0 Rh o Rh o ,hr',hr'' DCe D,C,e R 1 Rh 1 Rh o ,rh',hr'' DcE D,c,E R 2 Rh 2 Rho,hr',rh" DCE D,C,E, R z Rh z Rh o ,rh',rh" dce d,c,e r rh hr',hr" dCe d,C,e, r' rh' rh',hr" dcE d,c,E r" rh" hr',rh" dCE d,C,E r y rh y rh',rh" Page 455 of the postulated alleles seems to imply that the genetic basis of the Fisher-Race theory and nomenclature are not correct, but the use of this nomenclature has been retained, since it is easier to understand than any other. b. The second most common nomenclature is that proposed by Wiener, who theorized multiple alleles at a single complex locus, each locus determining its particular agglutinogen comprising multiple factors that were designated by bold-face type. The equivalents of the most common Rh factors in the Fisher-Race and Wiener nomenclature are shown in Table 24.2. c. Recent studies analyzing DNA from donors of different Rh phenotypes have found two structural genes within the Rh locus of Rh (D) positive individuals and only one present in Rh-negative persons. Therefore, one gene appears to encode the D protein and the other governs the presence of C, c, E, and e. C. Other Blood Groups. Several other blood group systems with clinical relevance have been characterized. Other than those caused by clerical error, most transfusion reactions are due to sensitization against alloantigens of the Rh, Kell, Duffy, and Kidd systems, of which the Kell system is the most polymorphic. In contrast, most cases of autoimmune hemolytic anemia involve autoantibodies directed to public antigens (antigens common to most, if not all, humans), such as the I antigen or core Rh antigens. D. Laboratory Determination of Blood Types 1. Reagents. Most reagents consist of monoclonal antibodies, usually of mouse origin, used individually or blended, and directed against the different blood group antigens that are used for blood group typing. A major advantage of the use of monoclonals is their specificity, minimizing the possibility of false-positive reactions due to additional contaminating antibodies found in human serum reagents. An important disadvantage derives from the fact that monoclonal antibodies react with a single epitope and the blood group antigens have multiple epitopes. Thus, individuals missing the epitope recognized by the antibody may be typed as negative. This problem is significantly reduced by using a blend of monoclonal antibodies, each one of them recognizing a different epitope of a given antigen. 2. Tests a. Direct hemagglutination is the simplest, preferred test. It is easy to perform with typing reagents containing IgM antibodies that directly agglutinate cells expressing the corresponding antigen. Reagents containing IgG antibodies can also be used in a direct hemagglutination test. In one approach, protein is added in relatively high concentration to the reagent for the purpose of dissipating the repulsive forces that keep the red cells apart. As a consequence, the red cells can be directly agglutinated by IgG antibodies. A second approach involves modification of the IgG antibodies by mild reduction of their interchain disulfide bonds to produce “unfolded” molecules, capable of direct agglutination of red cells. b. Indirect antiglobulin test. In general, reagents containing IgG anti- Page 456 bodies are used in an indirect antiglobulin test (see below) as a way to induce the agglutination of red cells coated with the corresponding antibodies. E. Direct and Indirect Antiglobulin (Coombs) Tests. In 1945, Coombs, Mourant, and Race described the use of antihuman globulin serum to detect red cell-bound nonagglutinating antibodies. There are two basic types of antiglobulin or Coombs tests. 1. The direct antiglobulin test is performed to detect in vivo sensitization of red cells or, in other words, sensitization that has occurred in the patient (Fig. 24.1). The test is performed by adding antihuman IgG (and/or antihuman complement, to react with complement components bound to the red cells as a consequence of the antigen-antibody reaction) to the patient's washed red cells. If IgG antibody is bound to the red cells, agglutination (positive result) is observed after addition of the antiglobulin reagent and centrifugation. The direct antiglobulin test is an aid in diagnosis and investigation of: hemolytic disease of the newborn; autoimmune hemolytic anemia; drug-induced hemolytic anemia; and hemolytic transfusion reactions. 2. The indirect antiglobulin test detects in vitro sensitization, which is sensitization that has been allowed to occur in the test tube under optimal conditions (Fig. 24.2). Therefore, the test is used to investigate the presence of nonagglutinating red-cell antibodies in a patient's serum. The test is performed in two steps (hence the designation indirect): a serum suspected of containing red-cell antibodies is incubated with normal red blood cells; and after washing unbound antibodies, antihuman IgG (and/or anticomplement) antibodies are added to the red cells as in the direct test. The indirect antiglobulin test is useful in: detecting and characterizing red-cell antibodies using test cells of known antigenic composition (antibody screening); crossmatching; and phenotyping blood cells for antigens not demonstrable by other techniques Figure 24.1 Diagrammatic representation of a direct Coombs test using anti-IgG antibodies. Page 457 Figure 24.2 Diagrammatic representation of an indirect Coombs' test. II. Blood Transfusion Immunology A. Blood Testing 1. Compatibility testing. Before a blood transfusion, a series of procedures needs to be done to establish the proper selection of blood for the patient. Basically, those procedures try to establish ABO and Rh compatibility between donor and recipient and to rule out the existence of antibodies in the recipient's serum which could react with transfused red cells. a. To establish the ABO and Rh compatibility between donor and recipient, both the recipient and the blood to be transfused are typed. b. To rule out the existence of antibodies (other than anti-A or anti-B), a general antibody screening test is performed with group O red cells of known composition, which are first incubated with the patient's serum to check for agglutination; if the direct agglutination test is negative, an indirect antiglobulin (Coombs) test is performed. 2. The cross-match. The most direct way to detect antibodies in the recipient's serum that could cause hemolysis of the transfused red cells is to test the patient's serum with the donor's cells (major cross-match). Page 458 a. The complete cross-match also involves the same tests as the antibody screening test described above. b. An abbreviated version of the cross-match is often performed in patients with a negative antibody screening test. This consists of immediately centrifuging a mixture of the patient's serum and donor cells to detect agglutination; this primarily checks for ABO incompatibility. 3. The minor cross-match, which consists of testing a patient's cells with donor serum, is of little significance and rarely performed, since any donor antibodies would be greatly diluted in the recipient's plasma and rarely cause clinical problems. 4. Implications of positive antibody screening for transfusion. Donor blood found to contain antibodies can be safely transfused as packed red cells, containing very little plasma. This is a routine blood bank procedure, and no whole blood units containing clinically significant red-cell antibodies are issued. Such blood is issued as packed red cells and the plasma is discarded. If a patient has a positive antibody screening test due to a clinically significant antibody, the antibody is identified using a panel of cells of known antigenic composition and antigen negative blood is selected for transfusion. B. Blood Transfusion Reactions. Transfusion reactions may occur due to a wide variety of causes (Table 24.3). Among them, the most severe are those associated with hemolysis, which may be life-threatening. A list of the causes of fatal transfusion reactions reported to the FDA from 1985–1987 is reproduced in Table 24.4. 1. The most frequent cause is an ABO mismatch due to clerical error, resulting in the transfusion of the wrong blood. 2. Transfusion of blood incompatible for other blood groups to a patient previously sensitized during pregnancy or as a consequence of earlier transfusions can also cause a hemolytic reaction. 3. Patients with autoimmune hemolytic anemia often have antibodies reacting with “public” antigens expressed by red cells from virtually all donors as well as their own, and are likely to develop hemolysis whenever a transfusion is administered to them. C. Hemolytic Reactions 1. Pathogenesis. Hemolytic reactions can be classified as intravascular or extravascular. a. Intravascular hemolytic reactions are triggered by the binding of preformed IgM antibodies to the red cells. i. IgM antibodies are very effective in causing the activation of the complement system. Massive complement activation by red-cell Table 24.3 Classification of Transfusion Reactions A. Nonimmune B. Immune 1. Red-cell incompatibility 2. Incompatibilities associated with platelets and leukocytes 3. Incompatibilities due to antiallotypic antibodies (anti-Gm or Am antibodies) Page 459 Table 24.4 Summary of Fatal Transfusion Reactions a Causes No. Hemolytic reactions ABO incompatible transfusions 29 Collection errors 7 Blood bank clerical errors 8 Blood bank technical errors 1 Nursing unit errors 11 Undetermined 2 Non -ABO incompatible transfusions b 6 No detectable antibody 3 Glycerol 1 Nonhemolytic reactions 26 Bacterial contamination 11 c Acute respiratory distress 9 Anaphylaxis 6 a Reported to the Food and Drug Administration from 1985 to 1987. b Including anti-Jk b , -c, Fy a , and -K. c In nine cases, the source of contamination was a platelet preparation. Source: Beig, K., Calhoun, A., and Petz, L.D. ISBT & AABB Joint Congress, Los Angeles, CA, 1990, Abstract S282. antibodies causes intravascular red-cell lysis, with release of hemoglobin into the circulation. Most of the free hemoglobin forms complexes with haptoglobin. ii. Due to the massive release of soluble complement fragments (e.g., C3a and C5a) with anaphylotoxic properties, the patient may suffer generalized vasodilatation, hypotension, and shock. iii. Because of the interrelationships between the complement and clotting systems, disseminated intravascular coagulation may occur during a severe transfusion reaction. iv. As a consequence of the nephrotoxicity of free hemoglobin, the patient may develop acute renal failure, usually due to acute tubular necrosis. This only happens when the amount of release hemoglobin exceeds the binding capacity of haptoglobin. b. Extravascular hemolytic reactions are caused by the opsonization of red cells with IgG antibodies. i. IgG red-cell antibodies can activate complement but do not cause spontaneous red-cell lysis. [...]... production of autoantibodies that react with public red-cell antigens? A α-Methyldopa B Cephalosporin C Penicillin D Phenacetin E Quinidine 24.4 The destruction of Rh-positive erythrocytes after exposure to IgG anti-D antibodies is due to: A Complement activation B Fc-mediated phagocytosis C C3b-mediated phagocytosis D C3d-mediated phagocytosis E A combination of Fc and C3b-mediated phagocytosis 24.5 In... it has been reported to be associated with intravascular hemolysis c The absorption of IgG-containing immune complexes to platelets is also the cause of drug-induced thrombocytopenia Quinine, quinidine, digitoxin, gold, meprobamate, chlorothiazide, rifampin, and the sulfonamides have been reported to cause this type of drug-induced thrombo-cytopenia 2 Adsorption of the drug onto the red cells Adsorption... (C) There can be cross-reaction between penicillin and the cephalosporins; both groups of antibiotics belong to the β-lactam group and therefore have to share part of their structure 24.6 (A) The maternal anti-A and anti-B isoagglutinins will function as a natural anti-red-cell antibody, destroying incompatible fetal red cells before there is an opportunity to induce the anti-D immune response The... antibodies directed to the drug, due either to previous adsorption of the drug to the red cell or to adsorption of preformed antigen-antibody complexes to the red cell, or (as it is the case in the hemolytic anemia associated with α-methyldopa) by anti-red-cell antibodies identical to those detected in true autoimmune hemolytic anemia How α-methyldopa causes the production of these antibodies is the subject... anti-IgGa Drug-coated RBC + serum; antibody is IgG Membrane modification causing nonimmunological adsorption of proteins Cephalosporins Asymptomatic Positive with a variety of antisera Drug-coated RBC + serum; no specific antibody involved Autoimmune α-methyldopa Hemolysis in 8% of patients taking this medication Strongly positive with anti-IgGa Normal RBC + serum Autoantibody to RBC identical to Ab... test using anti-IgG antibodies 24.2 (A) 24.3 (A) α-Methyldopa (Aldomet) induces a very unique type of hemolytic anemia in which the antibodies react with red-cell antigens of the Rh complex and not to the drug itself 24.4 (B) IgG anti-D antibodies do NOT cause complement fixation after binding to the red-cell membrane because the D antigen molecules are too spaced to allow the IgG molecules to form the... pregnancy is also recommended, in addition to the postpartum administration The rationale for this approach is to avoid sensitization due to prenatal spontaneous or post-traumatic bleeding Prenatal anti-D prophylaxis is also indicated at the time that an Rh-negative pregnant woman is submitted to amniocentesis and must be continued at 12-week intervals, until delivery, to maintain sufficient protection c... small complexes (Ag1.Ab 1-3 ), even when involving IgG1 and IgG3 antibodies, are able to diffuse easily into the extravascular compartment, but are usually nonpathogenic because of their inability to activate complement 3 The most potentially pathogenic IC are those of intermediate size (Ag 2-3 .Ab 2-6 ), particularly when involving complement-fixing antibodies (IgG1, IgG3) of moderate to high affinity However,... the microcirculation, allowing the diffusion of small- to medium-sized soluble IC to the subendothelial spaces (Fig 25.3) a The initial step is likely to be the activation of monocytes or granulocytes by immobilized IC, resulting in the release of vasoactive amines and cytokines Receptor-mediated interactions involving Fc receptors or complement receptors on endothelial cells could play the initiating... disease of the newborn was estimated to be about 0.5% of total births, with a mortality rate close to 6% among affected newborns prior to the introduction of immunoprophylaxis Recent figures are considerably lower: 0.15 to 0.3% incidence of clinically evident disease, and the perinatal mortality rate appears to be declining to about 4% of affected newborns 2 Ninety-five percent of the cases of hemolytic . chemotactic factor-A B. Leukotriene B-4 (LTB-4) C. Major basic protein D. Platelet aggregation factor E. Prostaglandin E2 23 .7 Of the following reagents, which one will be able to induce the release. contamination 11 c Acute respiratory distress 9 Anaphylaxis 6 a Reported to the Food and Drug Administration from 1985 to 19 87. b Including anti-Jk b , -c, Fy a , and -K. c In nine cases, the source. serum haptoglobin which decreases due to the uptake of hemoglobin-haptoglobin complexes by the reticulo-endothelial system. ii. Measurement of unconjugated bilirubin on blood drawn 5 to 7 hours