Vaccination can trigger NK cell activation via direct engagement of receptors on NK cells (e.g. adjuvant binding to TLR4) or via triggering of expression of IL-12, IL-18, and type I IFN. Activated NK cells produce IFN-◻, thereby promoting TH1 differentiation of CD4 T cells, IgG2a class switching by B cells, and enhancing antigen presenting functions of myeloid cells. NK cells make cytokines (e.g. GM-CSF) and chemokines (e.g. MIP-1◻) that facilitate recruitment of myeloid cells, granulocytes, and other lymphocytes.