Involved in the modulation of the mitochondrial apoptotic pathway by ensuring the accumulation of cardiolipin (CL) in mitochondrial membranes. In vitro, the TRIAP1:PRELID1 complex mediates the transfer of phosphatidic acid (PA) between liposomes and probably functions as a PA transporter across the mitochondrion intermembrane space to provide PA for CL synthesis in the inner membrane. Regulates the mitochondrial apoptotic pathway in primary Th cells. Regulates Th cell differentiation by down-regulating STAT6 thereby reducing IL-4-induced Th2 cell number. May be important for the development of vital and immunocompetent organs. a 1,2-diacyl-sn-glycero-3-phosphate(in) = a 1,2-diacyl-sn-glycero-3-phosphate(out) Forms a complex with TRIAP1 in the mitochondrion intermembrane space. Interacts with OPA1 and AIFM1. Highly expressed in fetal liver; less expressed in fetal brain, lung, and kidney. At the adult stage, expression is drastically reduced in the liver but highly expressed in the spleen, brain, lung, lymph nodes and peripheral blood leukocytes. Up-regulated in response to activation in primary T helper cells.