CD4 and infection: After infection, naïve CD4 T cells differentiate into type 1 T helper (Th1), Th2, Th17, T follicular helper (Tfh), or regulatory T cells (Treg) lineages, CD4+ Th1 cells are the major effector lineage that mediates chlamydia clearance via interferon-gamma (IFN−γ) secretion [3,6].