Fig. 1.

CD4⁺ T cell-dependent activation of NK cells in lymph nodes. Upon immunization or infection, DCs present antigen to naïve CD4⁺ T cells in lymph nodes draining the immunization or inoculation sites. This event results in the activation of T cells which secrete IL-2 and upregulate the high affinity IL-2 receptor and CD40L. Activated CD4⁺ T cells contribute to further maturation of DC and their secretion of IL-12. Both cytokines, IL-2 and IL-12, synergize to initiate NK cell activation which results in the secretion of IFN-γ and TNF-α, critical for the development of subsequent adaptive immune responses