A PROTECTIVE ROLE FOR T-LYMPHOCYTES IN ASBESTOS-INDUCED PULMONARY INFLAMMATION AND COLLAGEN DEPOSITION

Several lines of evidence have suggested that specific (i.e., lymphocyte) immunity plays a role in chemical-induced pulmonary diseases, including asbestosis. To evaluate the influence of cell-mediated immunity in pulmonary inflammation and fibrosis evoked by asbestos fibers, we compared the effects of asbestos in immunodeficient mice (Balb/c nu/nu and severe combined immunodeficient [C3H-SCID]), immunologically normal mice of the same genetic background, and immunodeficient mice reconstituted with syngeneic T lymphocytes. Increases in lavaged cell numbers occurred in asbestos-treated immunodeficient mice compared with asbestos-treated immunocompetent or immunodeficient mice that received T lymphocytes. Differential analysis of the collected cells in treated mice demonstrated a predominantly neutrophilic infiltrate that correlated with increased levels of leukotriene B-4 and prostaglandin E(2). There were no significant differences between immunocompetent and athymic asbestos-treated mice in bronchoalveolar lavaged total protein. However, asbestos-treated SCID mice revealed a significant increase in protein content and lactate dehydrogenase activity compared with asbestos-treated normal mice, which did not occur in T lymphocyte-reconstituted SCID mice. Fibronectin levels were elevated in asbestos-exposed athymic mice when compared with air-exposed athymic mice or asbestos-exposed immunocompetent mice. Both asbestos-treated athymic and SCID mice showed a significant increase in total lung hydroxyproline when compared with asbestos-treated immunocompetent mice. Lung hydroxyproline was also reduced in asbestos-exposed SCID mice after T lymphocyte reconstitution and, conversely, increased in T cell-depleted Balb/c mice. Microscopically, asbestos exposure was associated with both cellular and fibrogenic inflammatory responses with asbestos-exposed SCID mice, revealing a more severe cellular response than similarly exposed normal mice. Using polymerase chain reaction analysis to detect relatively rare mRNA species, the lungs from control and asbestos-treated animals appeared to have similar levels of mRNA transcripts for interferon-gamma, a T cell cytokine with putative antifibrotic activity. Taken together, these data indicate that T cells influence asbestos-induced lung damage by minimizing both the inflammatory and fibrotic responses and are consistent with a protective role for T lymphocytes in asbestosis.