It acts by inducing antimicrobial peptides in epithelial cells, neutrophils and macrophages28 and increases transcription of the innate immune protein (hCAP-18) which is capable of killing a wide variety of viral and bacterial pathogens.29 These findings are supported by the observation that vitamin D receptor polymorphisms (which decrease the bioavailability of vitamin D to the cell) are associated with more severe bronchiolitis30 and that defective control of vitamin D receptor-mediated cell signalling predisposes to severe respiratory syncytial virus bronchiolitis.31 Here, CAMP is linked to bronchiolitis.