l-Citrulline Metabolism in Mice Augments CD4+ T Cell Proliferation and Cytokine Production In Vitro, and Accumulation in the Mycobacteria-Infected Lung

Activation, recruitment, and effector function of T lymphocytes are essential for control of mycobacterial Infection. These processes are tightly regulated in T cells by the availability of l-arginine within the microenvironment. In turn, mycobacterial Infection dampens T cell responsiveness through Arginase induction in myeloid cells, promoting sequestration of l-arginine within the local milieu. Here, we show T cells can replenish intracellular l-arginine through metabolism of l-citrulline to mediate inflammatory function, allowing anti-mycobacterial T cells to overcome arginase-mediated suppression. Furthermore, T cell l-citrulline metabolism is necessary for accumulation of CD4⁺ T cells at the site of Infection, suggesting this metabolic pathway is involved during anti-mycobacterial T cell immunity in vivo. Together, these findings establish a contribution for l-arginine synthesis by T cells during mycobacterial Infection, and implicate l-citrulline as a potential immuno-nutrient to modulate host immunity.