F2RL1 and asthma: Interestingly, exposure to inhaled antigens with a PAR-2-activating peptide led to allergic sensitization, whereas exposure to Ag alone induced tolerance in BALB/c mice administered ovalbumin (OVA), suggesting PAR-2 activation in the airways at the time of inhaled antigen exposure to be capable of shifting the resulting immune response toward allergic sensitization and the development of asthma.