1. Unit 1 Nature of the Immune Response Part 5 Humoral Immune Response Terry Kotrla, MS, MT(ASCP)BB

2. Antigens and Antibodies An antigen is any substance which is recognized as foreign by the body AND is capable of provoking a specific immune response. It is capable of stimulating the formation of antibody and development of cell mediated immunity. Reacts specifically with antibodies or T- lymphocytes.

3. Physical Nature of Antigens Foreign nature Immune system must distinguish between “self” and “non-self”. Body is tolerant of its own components and does not initiation immune response against these. If natural tolerance disturbed immune reaction occurs against self, autoimmune disease. The greater the foreignness the greater the immune response.

4. Physical Nature of Antigens Molecular size Higher molecular weight (MW) is better antigen. Large size AND higher number and variety of antigenic sites stimulates greater antibody production. MW less than 10,000 daltons little or weak antigenicity.

5. Physical Nature of Antigens Molecular complexity and rigidity The more complex the better. Complex proteins better than large repeating polymers.

6. Physical Nature of Antigens Haptens are low molecular weight but if coupled to large carrier molecule can elicit antibody response.

7. Physical Nature of Antigens Genetic Factors Not all individuals within a species will show the same response to an antigen. “Responders” and “Non-Responders” Also wide variation between species.

8. Physical Nature of Antigens Route of Administration and Dose Oral, skin, intramuscular, IV, peritoneal – different administration required for stimulation. Recognition may not occur if the dose is too small. If dose is too large may cause “immune paralysis”.

9. Antigenic Determinants Also known as “epitopes” Actual structure recognized as foreign. Number of antigenic determinants varies with molecular size. Immune response directed against SPECIFIC determinant for antibody binding.

10. Antigen-Antibody Binding “Lock and Key” “Poor fit” may result in an antibody that won’t stay put OR an antibody that may react with more than one antigen – “cross-reactivity”. In serology cross-reactivity is a limitation of many tests.

11. Antigen-Antibody Binding

12. Humoral Immunity Results in production of proteins called “immunoglobulins” or “antibodies”. Body exposed to “foreign” material termed “antigen” which may be harmful to body: virus, bacteria, etc. Antigen has bypassed other protective mechanisms, ie, first and second line of defense.

13. Dynamics of Antibody Production Primary immune response Latent period Gradual rise in antibody production taking days to weeks Plateau reached Antibody level declines

14. Dynamics of Antibody Production Antibody production Initial antibody produced in IgM Lasts 10-12 days Followed by production of IgG Lasts 4-5 days Without continued antigenic challenge antibody levels drop off, although IgG may continue to be produced.

15. Secondary Response Second exposure to SAME antigen. Memory cells are a beautiful thing. Recognition of antigen is immediate. Results in immediate production of protective antibody, mainly IgG but may see some IgM

16. Humoral Immune Response

17. Dynamics of Antibody Production

18. Cellular Events Antigen is “processed” by T lymphocytes and macrophages. Possess special receptors on surface. Termed “antigen presenter cell” APC. Antigen presented to B cell

19. Basic Antibody Structure Two identical heavy chains Gamma Delta Alpha Mu Epsilon

20. Basic Antibody Structure Two identical light chains Kappa OR Lambda

21. Basic Antibody Structure

22. Basic Structure of Immunoglobulins

23. Papain Cleavage Breaks disulfide bonds at hinge region Results in 2 “fragment antigen binding” (Fab) fragments. Contains variable region of antibody molecule Variable region is part of antibody molecule which binds to antigen.

24. Papain Cleavage

25. Pepsin Breaks antibody above disulfide bond. Two F(ab’)2 molecules The rest fragments Has the ability to bind with antigen and cause agglutination or precipitation

26. Papain and Pepsin Cleavage

27. IgG Most abundant Single structural unit Gamma heavy chains Found intravascularly AND extravascularly Coats organisms to enhance phagocytosis (opsonization)

28. IgG Crosses placenta – provides baby with immunity for first few weeks of infant’s life. Capable of binding complement which will result in cell lysis FOUR subclasses – IgG1, IgG2, IgG3 and IgG4

29. IgG

30. IgA Alpha heavy chains Found in secretions Produced by lymphoid tissue Important role in respiratory, urinary and bowel infections. 15-10% of Ig pool

31. Secretory IgA Exists as TWO basic structural units, a DIMER Produced by cells lining the mucous membranes.

32. Secretory IgA

33. IgA Does NOT cross the placenta. Does NOT bind complement. Present in LARGE quantities in breast milk which transfers across gut of infant.

34. IgM Mu heavy chains Largest of all Ig – PENTAMER 10% of Ig pool Due to large size restricted to intravascular space. FIXES COMPLEMENT. Does NOT cross placenta. Of greatest importance in primary immune response.

35. IgM

36. IgE Epsilon heavy chains Trace plasma protein Single structural unit Fc region binds strongly to mast cells. Mediates release of histamines and heparin>allergic reactions Increased in allergies and parasitic infections. Does NOT fix complement Does NOT cross the placenta

37. IgE

38. IgD Delta heavy chains. Single structural unit. Accounts for less than 1% of Ig pool. Primarily a cell bound Ig found on the surface of B lymphocytes. Despite studies extending for more than 4 decades, a specific role for serum IgD has not been defined while for IgD bound to the membrane of many B lymphocytes, several functions have been proposed. Does NOT cross the placenta. Does NOT fix complement.

39. Cellular Immune Response Important in defending against: fungi, parasites, bacteria. Responsible for hypersensitivity, transplant rejection, tumor surveillance. Thymus derived (T) lymphocytes

40. Cell Mediated Reaction Helper T cells – turn on immune response Suppressor T cells – turn off immune response Cytotoxic T cells directly attack antigen

41. Cell Mediated Immunity

42. Lymphokines Mixed group of proteins Not identified chemically, classified based on biological activity. Cause aggregation of macrophages at site of infection Chemotaxis Activate macrophages to phagocytose. End result is amplification of inflammatory response and recruitment of immune cells to the site.

43. Lymphokines Contact between antigen and specific sensitized T lymphocyte necessary for lymphokine release. NOT antigen specific but immune reaction against one antigen may stimulate simultaneous protection from a second microorganism.

44. Control of the Immune Response Very complex Genetic control Within a species some genetic types are good antibody producers while others are not. Rabbits produce high levels of antibodies to proteins while mice do not.

45. Control of the Immune Response Cellular control Two branches of immune response, cellular and humoral. T and B cell cooperation necessary for antibody production. T cells play important role in regulating antibody production.

46. Control of the Immune Response Helper T-cells interact with antigenic molecule and release substances which stimulate B-cells to produce antibody. Suppressor T-cells are thought to “turn off” B-cells. Very fine balance between the action of helper and suppressor T-cells.

47. References and Resources http://www.biology.arizona.edu/immunology/tutorials/immunology/page2.html http://www.jdaross.cwc.net/humoral_immunity.htm http://academic.brooklyn.cuny.edu/biology/bio4fv/page/aviruses/cellular-immune.html http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect23.htm