CD4 and infection: In response to viral [20,21,22], parasitic [23,24,25,26], or bacterial [27,28] infections, CD4+ T cells predominantly differentiate into Th1 cells that produce inflammatory cytokines (i.e., IFN-γ and TNF-ɑ) and participate in cell-mediated immune responses, such as enhancement of the differentiation of naïve CD8+ T cells into cytotoxic T cells (CTL) for the clearance of infections of viral [20,21,29], bacterial [30,31,32], and parasitic [33,34] origins.