Adaptive Immunity to Bacteria

Overview

The adaptive and innate responses work together to destroy bacteria. The adaptive response ensures the innate response is carried out efficiently. There are two major branches of the adaptive immune response, humoral immunity and cell-mediated immunity.

Humoral

Humoral immunity includes complement activation of the classical pathway. It results in the production of IgM and IgG and makes the complement system more efficient.

Cell-Mediated

Cell-mediated immunity provides help for macrophages. It includes IgG production (T-helper type II (TH₂) cells and B cells), which improves phagocytosis by opsonisation. Infected macrophages are rescued by T-helper type I TH₁ cells when phagocytosis and digestion mechanisms fail to eliminate the pathogen.

Extracellular Infection

The response to extracellular infection involves complement and phagocytosis; B cell and T helper type II cell stimulation and the production of IgM, which activates the classical cascade. There is also class switching of IgM to IgG, which is a good opsonin and targets bacterial Fcγ receptor expressed by macrophages and neutrophils.

Vesicular Infection

During a vesicular infection, the infected macrophage secretes IL-12. IL-12 stimulates T-helper type I cells which release IFN-γ. IFN-γ then triggers the macrophages to kill the pathogens inside.

Also see Immunity to Bacteria

Originally funded by the RVC Jim Bee Award 2007