Abstract Stomatin-like protein (SLP)-2 is a mainly mitochondrial protein identified in proteome analysis of glycolipid-enriched membrane microdomains of mammalian cells, and modulates T cell activation. To study SLP-2 function we generated T cell-specific SLP-2 knockout (SLP-2 T-K/O) mice since conventional SLP-2 knockout mice were embryonic lethal at the pre-implantation stage. These mice showed reduced CD4+ T cell responses and decreased respiratory complex I and II+III activities. Our mechanistic studies suggest SLP-2 recruits prohibitins to cardiolipin (CL)-enriched domains in the mitochondrial inner membrane to form specialized CL-enriched membrane microdomains, required for optimal cellular respiration. We hypothesized SLP-2 functions in this manner to regulate the bioenergetics of T cells. Seahorse XF analysis revealed that although SLP-2 T-K/O cells showed unaltered total cellular and mitochondrial oxygen consumption rates (OCRs), they had significantly greater non-mitochondrial OCR, mitochondrial OCR uncoupled from ATP synthesis, and greater reliance on glycolysis (71% of mice). Surprisingly, SLP-2 T-K/O cells exhibited greater spare respiratory capacity, a phenomenon not due to differential sensitivities of cells to uncoupling agents. This new immunometabolic phenotype suggests SLP-2 may regulate assembly of functional respiratory supercomplexes. Bioenergetic and biochemical analyses of mitochondria are underway to establish the regulatory role of SLP-2 in T cell metabolism.