Pro-inflammatory cytokines in lung and blood during steroid-induced Pneumocystis carinii pneumonia in rats.

To gain more insight into the role of cytokines in Pneumocystis carinii pneumonia (PCP) we followed pro-inflammatory cytokine profiles in rats with steroid-induced PCP at 2-week intervals. The cytokines measured were immunoreactive interleukin-1beta (IL-1beta), bioactive interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-alpha). In vivo cytokine concentrations were determined in three compartments, i.e., bronchoalveolar lavage (BAL) fluid, lung homogenates, and plasma. Lipopolysaccharide (LPS) -stimulated cytokine production by alveolar cells and in whole-blood cultures was measured ex vivo. P carinii load and host inflammatory response, as determined by lung/body weight ratio and 111indium-IgG biodistribution were monitored throughout developing PCP. IL-1beta was elevated in lung homogenates (600, range <20-1260 pg/mL) and IL-6 in BAL fluid (48, range <20-115 pg/mL), whereas the pro-inflammatory cytokine concentrations were not increased in plasma. Thus in rats with PCP elevated pro-inflammatory cytokine concentrations were found to be restricted to the lung compartments. Corticosteroids did not significantly influence cytokine concentrations, but showed profound inhibitory effects on ex vivo cytokine production. The LPS-stimulated cytokine production by alveolar cells gradually decreased during the 6 weeks after the start of the steroid injections, whereas the production in whole blood cultures was immediately and completely suppressed.