AbstractEffective host defense against bacterial invasion is characterized by the vigorous recruitment and activation of inflammatory cells, which is dependent on the coordinated expression of both pro‐and anti‐inflammatory cytokines. In this review, we present evidence indicating that both C‐X‐C and C‐C chemokines are integral components of antibacterial host defense. Specifically, in vitro studies indicate that C‐X‐C chemokines [interleukin‐8 (IL‐8) and macrophage inflammatory protein 2 (MIP‐2)] and the C‐C chemokine macrophage inflammatory protein 1 alpha (MIP‐1α) augment the ability of polymorphonuclear leukocytes (PMNs) and alveolar macrophages, respectively, to phagocytose and killEscherichia coli.In addition, the intratracheal instillation ofKlebsiella pneumoniaein CD‐I mice results in time‐dependent production of MIP‐2 and MIP‐1α, and the inhibition of MIP‐2 bioactivity in vivo results in decreases in lung PMN influx, impaired bacterial clearance, and early mortality. Finally, the anti‐inflammatory cytokine interleukin‐10 (IL‐10) is also expressed within the lung during the evolution ofKlebsiellapneumonia, and neutralization of IL‐10 in vivo results in enhanced proinflammatory cytokine production, bacterial clearance, and increases in both short‐ and long‐term survival. In conclusion, our studies indicate that specific chemokines are important mediators of leukocyte recruitment and/or activation in bacterial pneumonia and that the expression of these chemokines is regulated by endogenously produced IL‐10.