CD4 and bacterial infectious disease: It is well known that CD4+ T cells play the most important role in M. tuberculosis infection; however, the role of CD8+ T cells during this bacterial infection has recently become clearer than in the past, beginning with peptide recognition that binds to major histocompatibility complex I and can secrete IL-12, IL-17, IL-2, IL-10, IFN-γ, TNF- α and TGF-β -, just like CD4+T cells.