CD44 and infection: Given the delay in leukocyte recruitment to the lungs early in infection with B. pertussis (Fig. 2), we hypothesized that the differential timing of lymphocyte recruitment may be attributed to the altered expression of mucosal associated TRs on circulating and lung resident emTh cells, as defined by CD4+/CD44+/CD45RBlow cells expressing α4β7 and α4β1 (Fig. 3A).