REGULATION OF NITRIC-OXIDE RELEASE BY MACROPHAGES AFTER INTRATRACHEALLIPOPOLYSACCHARIDE

We investigated the effect of intratracheal (i.t.) lipopolysaccharide (LPS) on alveolar macrophage release of nitric oxide. Mice received i. t. LPS at doses ranging from 1 to 100 mu g/100 g body weight and were killed at serial intervals for bronchoalveolar lavage. Control mice re ceived i.t. phosphate-buffered saline. We found that after i.t. LPS, t here was an early (1 to 3 days) influx of neutrophils followed by a la ter (5 to 7 days) influx of macrophages into the lungs. Alveolar macro phages lavaged from mice given i.t. LPS did not spontaneously release nitric oxide (measured as nitrite), but the capacity of these cells to release nitric oxide in vitro in response to interferon-gamma (IFN-ga mma) or LPS was markedly upregulated. Alveolar macrophages lavaged fro m mice given i.t. LPS but not i.t. phosphate-buffered saline also expr essed mRNA for inducible nitric oxide synthase as measured by semiquan titative reverse-transcription polymerase chain reaction. To investiga te possible mechanisms for cellular priming for increased nitric oxide release after i.t. LPS, mice were depleted of CD4(+) lymphocytes with an anti-CD4 antibody, Alveolar macrophages from CD4-depleted mice giv en i.t. LPS released significantly less nitric oxide in vitro in compa rison to macrophages from nondepleted mice. Additional mice were treat ed with neutralizing doses of anti-tumor necrosis factor or anti-IFN-g amma antibody before i.t. LPS. Pretreatment with each cytokine antibod y decreased but did not eliminate macrophage priming for nitric oxide release after i.t. LPS. We conclude that intratracheal LPS induces mRN A for nitric oxide synthase in alveolar macrophages; priming the cells for increased release of nitric oxide in vitro. This alteration in al veolar macrophage function is dependent upon host CD4(+) lymphocytes a s well as the cytokines tumor necrosis factor and IFN-gamma.