German researchers exposed pregnant mice to airborne barnyard microbes. (Studies in humans show children who are raised on farms develop fewer allergies than kids raised in nonfarming communities.) The exposure triggered a mild inflammatory response in the pregnant mice, which was measured by an increased expression of microbe-sensing receptors called TLRs and the production of immune system substances called cytokines. The exposed mice gave birth to offspring who were resistant to allergies caused by the microbes. The study was published in the Journal of Experimental Medicine. '... Studies have demonstrated that many factors affecting the initiation and course of respiratory allergies appear to act within a narrow window of opportunity, either prenatally and/or early in life. It is still unresolved, however, how protective signals are transferred from the mothers to the developing fetus,' the authors wrote in the paper. The paper adds 'a new twist' to the hygiene hypothesis, said experts from the Center for Child Health Research at the University of Western Australia, in a commentary published with the study. The allergy response in human tissues differs from mice, they cautioned, but more attention should be paid to maternal environmental exposures during pregnancy that might influence the health of the offspring. 