IL17A and chlamydia infectious disease: Given that IFN-γ-producing Th1 cells can gain GM-CSF signature, IL-17A+ CD4 T cells can differentiate into IFN-γ+GM-CSF+ pathologic Th17 cells upon IL-23 stimulation, and a separate ThGM subset has also been proposed, the origins of IFN-γ+GM-CSF+ double- and IFN-γ+IL-17A+GM-CSF+ triple-producing cells in Chlamydia infection remain unknown [54–56].