We previously reported that massive infiltration of neutrophils in C3H/HeN (C3H) mice could not efficiently control Chlamydia muridarum (Cm) infection and might contribute to the high susceptibility of these mice to lung infection. To further define the nature of neutrophil responses in C3H mice during chlamydial infection, we examine the expression of adhesion molecules and CD11b related to neutrophils infiltration and activation, respectively, following intranasal Cm infection. The results showed that the expression of selectins (E-selectin, P-selectin and L-selectin), and intercellular cell adhesion molecule-1 (ICAM-1) in the lung of C3H mice increased more significantly than in C57BL/6 (B6) mice, the more resistant strain. These results correlated well with the massive neutrophils infiltration in C3H mice. In contrast, CD11b expression on peripheral blood and lung neutrophils in C3H mice exhibited a significant reduction compared with B6 mice during the late phage of infection (day 14). These findings suggest that the high-level expression of adhesion molecules in C3H mice may enhance neutrophils recruitment to the lung, but the decline of CD11b expression on neutrophils may attenuate neutrophil function. Therefore, CD11b down-regulation on neutrophils may contribute to the failure of C3H mice to control chlamydial lung infection.