VMC 221: Veterinary Immunology and Serology (1+1)

CARDINAL FEATURES OF ADAPTIVE IMMUNE RESPONSES

• Both humoral and cell mediated immune responses to antigens have a number of fundamental properties
  • Specificity
  • Diversity
  • Memory 
  • Specialization
  • Self limitation 
  • Non reactivity to self
• Specificity
  • Specific immune response is highly specific for distinct antigens or even different parts of a single antigenic complex (protein, polysaccharide or other macromolecules).
  • Antigenic specificity is determined by epitopes, which are some specific areas or chemical groupings on the surface of antigen molecules. Epitopes are also called antigenic determinants.
• Diversity
  • The total number of antigenic specificities of the lymphocytes in an individual is called lymphocyte repertoire, which is extremely large.
  • Immune system can discriminate at least 10⁷ to 10⁹ distinct antigenic determinants because of variability in the structure of the antigen binding sites of lymphocyte receptors for antigens. This property of the lymphocyte repertoire is called diversity.
• Memory
  • Memory is the capacity of the sensitized lymphocytes to response more efficiently to the subsequent exposure to the antigen.
  • Memory cells produce secondary immune response. Plasma cells and B-lymphocytes are short lived and die because of apoptosis. But some B-lymphocytes become long-lived memory cells. On exposure to antigen, they proliferate and differentiate into plasma cells without undergoing further maturation.
  • The second type of memory cells consists of large dividing IgM producing cells. These cells exist in the germinal centers where presences of IL-2 and antigen or follicular dendritic cells are required for the survival of memory cells.
  • When a second dose of antigen is given the sensitized (previously exposed) memory cells respond promptly, the lag period is shorter and more antibody is produced (secondary immune response). IgG is produced more than IgM where as in primary immune response IgM is produced more than IgG.
  • Similarly memory T cells are better able to home to the sites of infection than the naïve T cells.
• Specialization
  • It is the capacity of immune system to respond in distinct and special ways to different microbes. Thus maximizing the anti-microbial defense mechanisms.
• Self-limitation
  • All normal immune responses wane with time after antigen stimulation and immune system return to its resting basal state in a process called homeostasis.
  • Immune response eliminate antigen, which provide stimulus for lymphocyte activation.
  • The activated lymphocyte also may die or differentiate into functionally quiescent memory cells.
• Non-reactivity to self
  • The specific immune system discriminates between ‘self’ and ‘non-self’ (foreign) and responds to only foreign materials to the host, which is antigenic.
  • Abnormalities in the induction of immune response against self -antigen (autogenous antigen) results in disorder called autoimmune disorder.