RORC encodes RORγ (t) transcription factor which is indispensable in development of IL‐17A‐producing cells, and hereditary congenital deficiency of the RORγ resulted not only in lack of Th17 and other IL‐17A‐producing cells, but also decrease of mycobacteria‐specific Th1 cells and life‐threatening infection of low‐virulent Mycobacterium bovis BCG vaccine strain. Here, IL17A is linked to infection.