Several studies on Chlamydia infection have shown that many cells can produce IFN-γ, including natural killer T (NKT) cells, Th1 (CD4) or Th1-like (such as CD8) cells, NK (killer ILC1s), ILC1s (helper ILC1s), Ex-ILC3s, mucosal-associated invariant T (MAIT) cells, and even some myeloid cells [23,24,25]. Here, CD4 is linked to chlamydia infectious disease.