Figure 1.

Graphic representation of the “desired” Th1-type immune response in animals protected against bovine anaplasmosis. Initial bodies released from the bovine erythrocyte encounter antigen-presenting cells (macrophages and/or dendritic cells), which engulf, process, and present epitopes to both B and T cells. CD4⁺ T cells are activated when they encounter the appropriate epitopes in the context of class II major histocompatibility receptors on antigen-presenting cells. These activated T cells secrete specific lymphokines, including IFNγ and IL-2. B cells are activated and stimulated by CD4⁺ T-cell cytokines and become IgG2-producing plasma cells. The large quantities of IgG2 can neutralize initial bodies, rendering them incapable of infecting normal erythrocytes. At the same time, activated macrophages destroy opsonized bacteria faster in the presence of IFNγ, leading to recovery from the clinical syndrome.