PTGS2 and asthma: According to our and others hypothesis, asthma develops partly as a result of improper regulation of COX-2 activity [28,29], and, given that PGE2 and PGI2 are considered anti-inflammatory protective prostanoids within the lungs [25,30], we speculate that PGE2 and PGI2, but not PGD2, attempt to trigger a beneficial compensatory phenomenon in mice exposed to HDM.