Sex Drives Dimorphic Immune Responses to Viral Infections

New attention to sexual dimorphism in normal mam-malian physiology and disease has uncovered a previ-ously unappreciated breadth of mechanisms by which females and males differentially exhibit quantitative phenotypes. Thus, in addition to the established mod-ifying effects of hormones, which prenatally and postpubertally pattern cells and tissues in a sexually dimorphic fashion, sex differences are caused by extra-gonadal and dosage effects of genes encoded on sex chromosomes. Sex differences in immune responses, especially during autoimmunity, have been studied pre-dominantly within the context of sex hormone effects. More recently, immune response genes have been local-ized to sex chromosomes themselves or found to be reg-ulated by sex chromosome genes. Thus, understanding how sex impacts immunity requires the elucidation of complex interactions among sex hormones, sex chromo-somes, and immune response genes. In this Brief Re-view, we discuss current knowledge and new insights into these intricate relationships in the context of viral infections.