Regulation of CD8⁺ T lymphocyte effector function and macrophage inflammatory cytokine production by retinoic acid receptor γ

Vitamin A and its derivatives regulate a broad array of immune functions. The effects of these retinoids are mediated through members of retinoic acid receptors (RARs) and retinoid X receptors. However, the role of individual retinoid receptors in the pleiotropic effects of retinoids remains unclear. To dissect the role of these receptors in the immune system, we analyzed immune cell development and function in mice conditionally lacking RARγ, the third member of the RAR family. We show that RARγ is dispensable for T and B lymphocyte development, the humoral immune response to a T-dependent Ag and in vitro Th cell differentiation. However, RARγ-deficient mice had a defective primary and memory CD8⁺ T cell response to listeria monocytogenes infection. Unexpectedly, RARγ-deficient macrophages exhibited impaired inflammatory cytokine production upon TLR stimulation. These results suggest that under physiological condition, RAR-γ is a positive regulator of inflammatory cytokine production.