We compared immunocompromised mice with normal mice during the airborne Klebsiella pneumoniae (KP) infection, to study the course and developing mechanisms of KP pneumonia. There are significant difference in the number and peaking time of PMN, the number of lymphocytes and plasma cells in the bronchoalveolar lavage fluids of different mice groups. These results indicate that the interference of immune specific and nonspecific host responses is an important variable in antibiotic efficacy and the existence of an immunomodulating cytokine network was suggested.