Adaptive Immunity to Bacteria

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

• Complement activation of the classical pathway
  • Production of IgM and IgG makes the complement system more efficient

Cell-Mediated

• Help for macrophages
  • IgG production (T-helper type II cells and B cells) which improves phagocytosis by opsonisation
  • Infected macrophages are rescued by T-helper type I cells when phagocytosis and digestion mechanisms fail to eliminate the pathogen

Extracellular Infection

• Complement and phagocytosis

• B cell and T helper type II cell stimulation

• Production of IgM which activates the classical cascade

• Class switching of IgM to IgG which is a good opsonin and targets bacterial Fcγ receptor expressed by macrophages and neutrophils

Vesicular Infection

• The infected macrophage secretes IL-12

• IL-12 stimulates T-helper type I cells which release IFN-γ

• IFN-γ triggers the macrophages to kill the pathogens inside

Also see Immunity to Bacteria