Role of interleukin-8 in community-acquired pneumonia: Relation to microbial load and pulmonary function

Summary In pneumonia local phagocyte activation is crucial for clearing of pathogenic microorganisms. In this context alveolar macrophage interleukin-8 secretion, phagocyte oxidative response and concentrations of lavage proteins were quantified, including interleukin-8, in 31 patients with pneumonia, 13 age matched patients with peripheral lung consolidation and six healthy volunteers; these findings were related to the impairment of gas exchange and the bacterial load in the alveolar space. Increased interleukin-8 levels were found in bronchoalveolar lavage fluid (BALF) and in alveolar macrophage supernatants from patients with pneumonia (214 ng/10⁵ AM±121 vs 71 ng/10⁵ AM±35 and 66 ng/10⁵ AM±30, p<0.05). Interleukin-8 release from alveolar macrophages correlated with the upregulated spontaneous luminol enhanced oxidative response of pulmonary phagocytes but not with the neutrophil count in BALF. In pneumonia patients a significant difference was found between patients with 10⁴ or more colony forming units (CFU)/ml BALF of one pathogen and patients with less CFU or nonspecific microbiological results (261 ng/10⁵ AM±89 vs 179 ng/10⁵ AM±81 and 7.5 ng/ml BALF±17 vs 0.44 ng/ml BALF±1, p<0.05). Further, a negative correlation between interleukin-8 release of alveolar macrophages and the arterial pO₂ at the time of BALF could be demonstrated (r=–0.47, p<0.05). The results demonstrate local cellular activation in community-acquired pneumonia, which is related to the bacterial load in the alveolar space and to impairment of gas exchange. This is consistent with the hypothesis that pulmonary phagocytes play a central role in the pathogenesis of bacterial pneumonia, contributing not only to bacterial clearing but also to local tissue damage.