6.2.3 Activation of T lymphocytes

Activated T helper cells proliferate and differentiate into effector cells with the help of cytokines. Interleukin-2, secreted by T-helper cells modulate the clonal expansion of activated T lymphocytes. The effector cells help in killing the pathogen by phagocytosis.

Activated cytotoxic T cells kill the intracellular pathogens in the cytoplasm of infected cells. Alternatively, cytotoxic T cells eliminate the infection by phagocytosis of the infected cells.

6.2.4 Activation of B lymphocytes

B cells are activated with the help of CD4+ T lymphocyte and differentiated into antibody secreting plasma cells. Usually lipids and carbohydrate antigens stimulate the production of IgM class of antibody while protein antigens can induce IgG, IgA, IgE type of immunoglobulins. The production of different form of antibodies requires class switching of the surface immunoglobulin present over the B cells. Antibodies bind and prevent the pathogens, thus “neutralizing” the pathogens and block their ability to infect host cells. IgA antibodies specifically act on the mucosal surface of the gastrointestinal and respiratory tract and neutralize the invading pathogens. IgG antibodies coat pathogens and target them for phagocytosis while IgM can activate the complement pathway.

6.2.5 Production of memory cells

Initial activation of T lymphocyte produces the long-lived memory cells that survive for many days following infection. Memory cells respond much faster than the naïve lymphocytes. Generations of long lasting memory cells are the major target for vaccine design against microbial pathogens.