Sex differences in infectious diseases-common but neglected.

Women and men are different-and this fundamental observation extends to their susceptibility and response to different diseases, including autoimmune and infectious diseases. Apart from cultural and behavioral differences between the sexes that play a prominent role in the exposure to pathogens, increasing data show that women and men also differ in their immune responses to infections. This applies to infections with viruses, bacteria, and parasites, including the pathogens most relevant for human health, causing malaria, tuberculosis, AIDS, hepatitis, and influenza. Only recently, the biological pathways responsible for these sex-based differences in the manifestations of infectious diseases have been started to be unveiled. These include immunological pathways affected by sex hormones, as well as consequences of differential expression of X-chromosome-encoded genes on immune responses to pathogens. Further research is required to gain a better understanding of the differences in immunity to infections between women and men in order to develop individualized treatment concepts in infectious diseases that take sex-specific host factors into account.