CD4 and infection: CD4+ T cells, or T helper cells (Th), play a central role in immune protection, by inducing (i) long-term maintenance of antigen-specific CD8+ memory T cells, (ii) antibody production from B cells, (iii) macrophages to develop enhanced microbicidal activity, to recruit neutrophils, eosinophils, and basophils to sites of infection and inflammation, and (iv) expression of cytokines and chemokines to orchestrate the full panoply of immune responses.