Figure 1. B cell and CD4 T cell interaction.

A. Naïve T cells are generally primed by antigen-presenting cells such as dendritic cells. B. Antigen-specific T cells recognizing antigens presented by B cells stimulate the B cells through CD40 ligand (CD40L) interactions with CD40. C. Activated B cells upregulate costimulatory molecules such as B7.2 and B7.1 which are then able to stimulate T cells. D. T cells activated by specific antigen-recognition together with costimulation produce cytokines. E. T cell-derived cytokines stimulate B cells to switch isotypes and differentiate to produce antibodies.