drmsaiem IMMUNOGLOBULINS DR. Mohammed Saiemaldahr FACULTY OF APPLIED MEDICAL SCIENCES KAAU

drmsaiem BIOLOGICAL & CHEMICAL PROPERTIES OF Igs IgG. Is the major immunoglobulin in human serum, accounting for approximately 75%. Concentration of approximately 1200 mg/dl. IgG is a monomer consisting of identical pairs of H and L chains linked by disulfide bridges. Four subclasses of IgG have been identified, based on H chain differences: IgG1, IgG2, IgG3, and IgG4. IgG is the only immunoglobulin that can cross the placenta in humans and protect the infant during the first months of life. IgG molecules are capable of binding complement by the classical pathway (except for the IgG4, which activate by the alternative pathway).

drmsaiem BIOLOGICAL AND CHEMICAL PROPERTIES OF IMMUNOGLOBULINS IgG is the major antibody produced in the secondary immune response IgG has a half-life of approximately 21 days Effective antitoxic immunity is exclusively IgG. IgG is the major opsonizing immunoglobulin in phagocytosis; neutrophils have receptors for the Fc fragments of IgG I and IgG 3.

drmsaiem BIOLOGICAL & CHEMICAL PROPERTIES OF Igs IgM. Represents about 8% to 10% of the total serum Igs. Concentration of ≈ I2O mg/dl. IgM has a pentameric structure consisting of five monomer units linked by a J chain and by disulfide bonds at the Fc fragment. IgM is easily dissociated by reducing agents, forming five monomeric units.

drmsaiem BIOLOGICAL AND CHEMICAL PROPERTIES OF IMMUNOGLOBULINS IgM is the first antibody that an immunologically committed B lymphocyte can produce. It has a half-life of approximately 10 days. IgM is the predominant antibody in the early (primary) immune response to most antigens. IgM is the only antibody made to certain carbohydrate antigens, such as the ABO blood group antigens on human erythrocytes. IgM is the most efficient immunoglobulin at activating complement in lytic reactions.

drmsaiem Allo-antibodies & Auto-antibodies Antigens that initiate the immune cascades results in the formation of either allo-abs or auto-abs. Allo-antibodies are produced after exposure to genetically different or non-self, antigens of the same species. Auto-antibodies are produced in response to self antigens.

drmsaiem Factors Influence Agglutination Reaction Concentration of Ag-Ab The agglutination reaction is influenced by the, concentration of both Ag and Ab as well as other factors such as pH, temp. ionic strength, surface change, Ab class, red cell Ag dosage, the use of various enhancement media Under ideal reaction conditions, an equivalent amount of Ag and Ab bind in optimal proportions.

drmsaiem Factors Influence Agglutination Reaction Prozone effect: an excess of either Ag or Ab, may lead to unbound immunoglobulin Postzone effect: surplus (excess of Ag-binding sites) In prozone or postzone effect the lattice formation and subsequent agglutination may not occur in the test system, leading to the assumption of false negative results. To correct the problem of excessive Ab, the serum may be diluted with each serial dilution of serum tested against red cells. To correct the problem of excessive Ag, the serum to cell-ratio in the test system may be in which will tend to increase the number of Abs available to bind with red cell.

drmsaiem Factors Influence Agglutination Reaction Effect of pH The ideal pH is between 6.5 and 7.5, exceptions to this range include some examples of Anti-M, and some Abs of the Pr (SP1) group which show stronger reactivity below pH 6.5.

drmsaiem Factors Influence Agglutination Reaction Temperature Different types of Abs may exhibit optimal reactivity at different temp. IgM Abs usually react optimally at or below 22°C. IgG Abs usually require 37°C temp. The Ag-Ab reactions are exothermic (heat is given up), therefore, Abs binds to a greater degree at low temperature

drmsaiem Laboratory Examination of Reaction between Ags and Abs In vitro testing for the detection of Ags or Abs may be accomplished by a variety of immunologic techniques. Such techniques as agglutination, precipitation, agglutination inhibition, and hemolysis are the most commonly used methods to detect the presence of blood group Ags or Abs. In blood bank testing, agglutination reactions are the major manifestation of the blood group Ag-Ab response. Typing for ABO, Rh, and other blood group Ags is accomplished by agglutination reaction.

drmsaiem Laboratory Examination of Reaction between Ags and Abs There are two stages for agglutination to develop; Stage 1: known as sensitization, Ab binding occurs. Antigenic determinants on the red cell membrane combine with the antigen combining site (Fab region) on the variable regions of the immunoglobulin heavy and light chains. Stage 2: a lattice structure composed of multiple Ag-Ab bridges between Abs and red cell Ags is formed visible agglutination is present during this stage.