Local delivery of the viral interleukin-10 gene suppresses tissue inflammation in murine Pneumocystis carinii infection

The relationship between tissue inflammation and clearance of the opportunistic pathogen Pneumocystis carinii is poorly understood. We asked whether the anti-inflammatory cytokine interleukin-10 (IL-10) is released during the host response to infection with P. carinii and whether local delivery of the IL-10 gene could suppress tissue inflammatory responses without compromising clearance of infection. Control and CD4-depleted mice were inoculated with P. carinii, and at serial intervals after inoculation, lung tissue was assayed for IL-10 by enzyme-linked immunosorbent assay. We found that IL-10 was released in lung tissue in control mice and was present in higher concentrations in CD4-depleted mice with progressive infection. Control and CD4-depleted mice were then pretreated with 10⁹ PFU of intratracheally administered adenoviral vector containing the viral IL-10 gene or the luciferase gene followed by inoculation with P. carinii. Pretreatment with viral IL-10 did not alter clearance of infection in control mice or severity of infection in CD4-depleted mice but did decrease tissue inflammation. We then asked whether gene transfer of viral IL-10 could decrease tissue inflammation during immune reconstitution. In these experiments, immunodeficient scid mice were inoculated with P. carinii and were heavily infected after 4 weeks. When these mice are immunologically reconstituted by intravenous administration of spleen cells from normal mice, a hyperinflammatory reaction developed in lung tissue, associated with high mortality. In comparison to control mice, mice treated with viral IL-10 prior to reconstitution showed significantly decreased lung wet weight, bronchoalveolar lavage fluid (BALF) lactate dehydrogenase, and BALF neutrophils. In contrast, infection intensity, as measured by PCR for P. carinii rRNA, was unchanged between the IL-10 and luciferase groups. Survival was also improved in the IL-10-treated mice. We conclude that release of IL-10 is part of the host response to infection with P. carinii and that gene therapy with viral IL-10 can lessen excessive tissue inflammation without altering pathogen clearance. In the setting of immune reconstitution and P. carinii pneumonia, pretreatment with the viral IL-10 gene decreases excessive tissue inflammation and improves survival. These results are relevant to acute respiratory failure after initiation of antibiotic treatment for human P. carinii pneumonia and to immune reconstitution syndromes in human immunodeficiency virus-positive patients started on highly active antiretroviral therapy.