Hunting for histamine's source

For asthma sufferers, contracting a lung infection can mean hospitalization, but it has never been clear how bugs exacerbate allergic conditions. Xu et al. (page 2907) now show that the major allergic inflammatory mediator—histamine—is also produced in response to infection. But it comes from an unexpected source.

Mast cells together with basophils are considered the major producers of histamine. Because bacterial infection of the lung can lead to asthma attacks more severe than those caused by allergens, Caughey's group hypothesized that histamine might be produced in response to infection and, if indeed it were, that mast cells were likely to be the source.

The team found that, approximately one week after infection with Mycoplasma pulmonis bacteria, histamine levels in the lungs of the mice had risen dramatically. However,...