( mice because the infection wouldn't be...)White blood cells in lung produce histamine seen in allergies

The reason was straightforward, Caughey says. Neutrophil numbers increased in response to infection, and neutrophils in turn produced histamine. "It's a direct effect of the mycoplasma bacteria on neutrophils. They induce neutrophils to produce the enzyme that produces histamine."

Individual neutrophils produce much less histamine than individual mast cells, says Caughey, but "because pus contains millions if not billions of neutrophils, the overall amount they make is very considerable."

The neutrophil-histamine effect was similar in the wild-type mice, reports Caughey: "Histamine levels from neutrophils blew right past the histamine levels contributed by mast cells."

The wild-type mice suffered less severe infections overall because "as a number of recent studies, including ours, have shown, mast cells actually play a role in protecting against bacteria," Caughey explains. "For example, a mouse without mast cells with the equivalent of a ruptured appendix will die of the resulting infection, while a mouse with mast cells can survive."

When the infected mice without mast cells were given antihistamines, the level of histamine, and therefore the severity of the pneumonia, dropped in proportion to the amount of antihistamine given.

"This is a study in mice, so we cannot freely extrapolate the results to human beings," cautions Caughey. "Nonetheless, antihistamines may deserve more of a look as therapeutic options in lung and airway infection."

He says the study also has implications for other types of airway infection "in which there are a lot of white blood cells –?cystic fibrosis, for example, which can be associated with asthma-like airway contraction."

The next steps for Caughey a
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Source:University of California - San Francisco