Vitamin D mediates a key antimicrobial response in humans against Mycobacterium tuberculosis (TB), according to a new study in Science. The findings may help explain why African-Americans, who tend to carry lower levels of vitamin D, are more susceptible to TB.The authors "were able to provide the complete series of molecular events that explains why African-American populations have enhanced susceptibility to TB and have a much more aggressive disease course," said John White at McGill University in Montreal, who did not participate in the study.As part of the innate immune system, microbial clues such as bacterial lipopeptides activate mammalian Toll-like receptors (TLR), which trigger an antimicrobial response in monocytes. In mice, this process is mediated by nitric oxide. However, the study authors, based at the University of California at Los Angeles, found in an earlier study that inhibiting NO had no effect on the human pathway.To investigate, the team,...

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