The T-cell immune regulator 1 (TCIRG1) is the a3 subunit of the vacuolar-type proton transporting ATPase (V-ATPase), a proton pump in late endosomes and lysosomes that functions in the luminal acidification of these organelles. Genetic defects in the gene encoding this protein a responsible for a severe form of autosomal recessive osteopetrosis, a condition that leads to increased bone density, decreased bone strength, and inflammation in bone tissues. TCIRG1 is also required for the normal secretion of insulin and the bacteria-killing function of macrophages.Synonyms: ATP6V0A3, Osteoclastic proton pump 116 kDa subunit, T-cell immune regulator 1, T-cell immune response cDNA7 protein, V-ATPase 116 kDa isoform a3, V-type proton ATPase 116 kDa subunit a isoform 3, Vacuolar proton translocating ATPase 116 kDa subunit a isoform 3