PTGS2 and Allergy: Thus, in the absence or reduction of COX-2, the flux through the 5-LOX pathway may be increased, as reported by studies of lungs from Cox-2 null mice that had an increased inflammatory response to an allergy challenge compared to wild-type mice [25], and by administration of Cox inhibitor in rats that led to an increase in levels of the leukotriene LTB4[24].