FIGURE 1.

B cells as activators of cellular immunity. B cells are initially activated by antigen recognition through BCR. Internalized antigens are then presented through class II MHC to CD4⁺ helper T cells, which provide co-stimulatory signals for B cell activation. Activated B cells acquire enhanced potential for antigen presentation with upregulation of MHC-I and II and co-stimulatory molecules, such as CD80/86, further activating both CD4⁺ and CD8⁺ T cells. Also, CD27 is upregulated in activated B cells, and interaction between this molecule and CD70 on the membrane of memory CD8⁺ T cells promotes their maintenance and facilitates their activation in an antigen-independent manner. CD8⁺ T cell activation leads to efficient cell proliferation and production of potent inflammatory mediators, such as granzymes, perforin, and IFN-γ.