Role of virus replication in a murine model of AIDS-associated interstitial pneumonitis

One of the major complications of HIV infection is the development of interstitial pneumonitis (IP). IP is characterized by lymphocytic infiltration of the lung and may lead to respiratory failure in some cases. The etiology of IP is unknown although it is likely the result of an antiviral or autoimmune response occurring in the lung. To determine the role of viral replication in the development of IP, AZT was evaluated for the ability to inhibit development of lung inflammation in a murine model of retrovirus-associated IP. Mice were infected with LP-BM5 retrovirus, which induces murine AIDS. Infected mice develop IP by 4 weeks postinfection characterized by infiltration of the lung with activated T cells, B cells, and macrophages. Virus could be detected in the lungs of these mice by 2 weeks postinfection and persisted throughout the course of disease. To determine if reduction in viral load affected the disease process, infected mice were treated with AZT for varying periods postinfection and analyzed for the development of IP. Treatment with AZT resulted in a treatment time-dependent reduction of viral RNA in the lungs of infected mice compared to untreated infected mice. The reduction of viral burden in the lungs correlated with a reduction in the severity of IP and decreased production of the proinflammatory cytokines interleukin (IL)-1 beta and interferon (IFN)-gamma. These results suggest that continuous viral replication in the lung contributes to the pathogenesis of IP.

Role of T cell subsets in the development of AIDS-associated interstitial pneumonitis in mice

Idiopathic interstitial pneumonitis (IP), characterized by lymphocytic infiltration of the lung and pulmonary dysfunction, is a major noninfectious complication of human immunodeficiency virus (HIV) infection. The role of the CD4+ and CD8+ T cell populations and INF-gamma in the development of IP were analyzed using a murine model of retroviral-associated IP. Infected mice depleted of CD8+ T cells developed IP similarly to untreated infected mice, suggesting that the CD8+ T cell population does not play a role in IP. Furthermore, depletion of CD8+ T cells did not alter the level of viral RNA in lungs, suggesting that cytotoxic T cells may not serve a role in controlling virus burden in lungs. In contrast, depletion of CD4+ T cells in infected mice prevented the development of IP and inhibited inflammatory cytokine expression, suggesting that CD4+ T cells are important for the development of IP. IFN-gamma -/- mice infected with virus for 10 weeks developed IP, although the severity of lymphocytic infiltration was substantially reduced compared to infected wild-type mice. The data suggest that persistent viral antigen in the lung may drive a CD4+ T cell-mediated immune response, resulting in the chronic production of IFN-gamma which amplifies a chronic inflammatory response in the lung resulting in tissue injury.

Pulmonary lymphoid cell activation and cytokine expression in murine AIDS-associated interstitial pneumonitis

Limited information is available about the pathogenesis of acquired immune deficiency syndrome (AIDS)-associated idiopathic interstitial pneumonitis, a common noninfectious complication of human immunodeficiency virus (HIV) infection. Infection of C57B1/6 mice with LP-BM5 retrovirus, a murine model of AIDS, leads to development of a diffuse interstitial pneumonitis that displays many features of human AIDS-associated interstitial pneumonitis. To further characterize the cellular and molecular features of this lung disease, the temporal development of cellular infiltration, cytokine expression, and virus replication were evaluated in lung tissue of virus-infected mice. Persistent expression of viral RNA was detectable in lungs as early as 1 wk after infection. Infiltration of the lungs by CD4+ and CD8+ T cells, by IgG+ and IgA+ B cells, and by macrophages was observed by 4 wk after infection and continued through 8 wk of infection. Histologically, cellular infiltration was most pronounced in peribronchial and perivascular regions, whereas inflammation of alveolar septae and alveolar spaces was minimal. In contrast to normals, T cells from infected lungs were immunodeficient in that they failed to proliferate in response to the mitogen concanavalin A (ConA). However, evaluation of cytokine mRNA expression by interstitial lung lymphoid cells indicated that cells from infected lungs were chronically activated, in that elevated expression of interferon-gamma (IFN-gamma) and interleukin-10 (IL-10) was observed throughout the course of infection. Similarly, expression by interstitial lung lymphoid cells of mRNA for the proinflammatory cytokine IL-1 and the fibrogenic cytokine transforming growth factor-beta (TGF-beta) was also increased following infection. These results indicate that retrovirus-induced immunodeficiency in mice is associated with infiltration and chronic activation of lymphoid cells in the lungs. Furthermore, simultaneous expression of IL-10, IFN-gamma, and TGF-beta suggests that cytokine-expressing cells in infected lungs may be unresponsive to inhibitory and antiinflammatory effects of IL-10 and/or TGF-beta, thus contributing to chronicity of inflammation in this disorder.