This document discusses humoral immunity and antibodies. It describes how antibodies are produced by B cells and plasma cells in response to antigens. The primary role of antibodies is protection against reinfection by binding to pathogens and marking them for destruction or neutralization. The document provides details on antibody structure, classes, properties, functions, and role in immune responses.

2. HUMORAL IMMUNITY Antibody mediated Part of Specific immunity along with cell-mediated type When Nonspecific immunity fails, tissue macrophages take up the organisms specific immune responses activated Antibody is synthesized

3. HUMORAL IMMUNITY Primary molecular component: antibody Ab is made by B-cells and plasma cells in response to Ag challenge Ab: protection vs rechallenge block spread of agent in blood facilitate elimination of infectious agent Ab must also interact with host cells (macrophage, complement) Ab also serve as B-cell receptors to stimulate plasma cell growth and produce more Abs

5. HUMORAL IMMUNITY General Properties of an Antigen: Foreignness Chemical composition > CHONs are best immunogens, CHOs are weak; Lipids and nucleic acids: poor Molecular size 500-1000 Da= min size for immunogenicity <10,000 Da = weak immunogen >10,000 Da = strong immunogen

6. HUMORAL IMMUNITY General Properties of an Antigen: Chemical Complexity Response to Ag may vary according to: Genetic composition of the host Method of administration and dose

8. HUMORAL IMMUNITY ADJUVANT: when mixed with Ag enhances duration and magnitude of the immune response by: Prolonging retention of immunogen Increasing effective size of immunogen Stimulating local influx of macrophages and/or other immune cell types to the injection site. Ex. Freund’s adjuvant, liposomes, bacterial cell wall components, molecular cages for Ag and polymeric surfactant, E.coli, cholera toxin

9. HUMORAL IMMUNITY Immunogen = substance capable of eliciting an immune response Antigen = substance recognized by immune response Epitope = Molecular structure recognized by immune response Hapten = incomplete immunogen that cannot initiate response but that can be recognized by Ab

10. HUMORAL IMMUNITY Carrier = protein modified by hapten to elicit response Adjuvant = substance that promotes immune response to an Ag T-independent Ags = Ags with large repetitive structures (e.g., bacteria, flagellin, lipopolysaccharide, polysaccharide) T-dependent Ags = Ags that must be presented to T and B cells for Ab production

12. HUMORAL IMMUNITY Immune Component: Fc Receptor Interaction: macrophage (opsonization) PMNs (opsonization) T cells (activation) NK cells, ADCC (killing) Mast cells for IgE (allergic reactions, anti-parasitic)

13. HUMORAL IMMUNITY Immune Component: Complement Interaction: Complement system Function: Opsonization Killing (especially bacteria)

15. HUMORAL IMMUNITY Antimicrobial Action of Antibodies: Opsonic; promote ingestion and killing by phagocytic cells Neutralize (block attachment) toxins and viruses Agglutinate bacteria; may aid in clearing Render motile organisms nonmotile

16. HUMORAL IMMUNITY Antimicrobial Action of Antibodies: 5. Combine with Ags on the microbial surface, activate complement cascade, thus inducing an inflammatory response, bringing fresh phagocytes and serum Abs into the site 6. Combine with Ags on the microbial surface, activate complement cascade, anchor the membrane attack complex (C5b to C9)

19. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 1. IgD > exists primarily as membrane/surface IgD on B-cell, along with IgM they are the only isotypes expressed by the same cell > no known biologic function > less than 1% of serum Igs > 185 kDa molecular mass

20. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 2. IgM > first Ab produced versus Ag challenge > can be produced in T-independent manner > 5-10% of total Igs in the adult > half life 5 days > pentameric: 5 units joined by disulfide bonds and the J chain (900 kDa)

21. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 2. IgM > theoretically has 10 Ag binding sites; > binds complement the best (1 pentamer activates the classic pathway) > Monomeric IgM is with IgD on surface of B cells > cannot go from blood to tissue because of size

22. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 2. IgM > immunity vs polysaccharide Ags (capsules) > promotes phagocytosis and bacteriolysis through complement activation > major component of rheumatoid factors

23. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 3. IgG > about 85% of all Igs in the adult > half life of 23 days (longest) > molecular mass of 184 kDa > 2 L chains of 22,000 Da and 2 H chains of 55,000 Da each > 4 subclasses: IgG 1-4, diff structure, relative concentration and function

24. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 3. IgG > production is T-cell dependent; can cross the placenta > principal Ig in booster and anamnestic response > high binding capacity for Ags, fixes complement, stimulates chemotaxis and acts as opsonin

26. Cross-reactive antibodies May react with more than 1 microorganism when they share similar Ag’ic determinants Historically called Natural antibodies Immune properties well documented in lab animals Often directed against polysaccharides with similar structures across different species, genera and families

27. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 4. IgA > 5-15% of all Igs in the adult > half life of 6 days > molecular mass of 160 kDa, basic 4-chain monomer, but can occur as dimers, trimers or multimers thru the J chain > Secretory Iga = appears in body secretions for local immunity

28. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 4. IgA > production requires T-cell help and mucosal stimulation by adjuvants like cholera toxin and attenuated salmonella > binds to poly-Ig receptors on epithelial cells for transport across cells > remains bound to IgA and cleaved to become Secretory Component once secretory IgA is secreted

29. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 4. IgA > about 2 gms of IgA/day secreted by adults > appears in colostrum, intestinal and respiratory secretions, saliva, tears and other secretions > IgA-deficient persons have more frequent respiratory tract infections

30. Pneumonia in IgA Deficiency

31. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 5. IgE > less than 1% of total serum Igs in adults > half life of about 2.5 days > most are bound to Fc receptors on mast cells and serve as receptors for allergens and parasite Ags > once Ige is bound by Ag, mast cells release histamine, prostaglandin, platelet activating factors and cytokines

32. HUMORAL IMMUNITY Immuneglobulins (Antibodies) 5. IgE > serve as protection versus parasitic infections > responsible for the manifestations of anaphylactic (Type 1) hypersensitivity

33. Anaphylactic shock

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