Our proposal is devoted to defining the pathogenesis of HIV infection in the lung. It describes a series of in vivo and in vitro experiments oriented towards constructing mechanistic mathematical models to better understand cytokine networks and their role in the dynamics of HIV replication in the lung. Deciphering cytokine networks and their differential and combined effects on HIV-1 (HIV) replication in the lung presents a problem of enormous complexity. Our studies clearly show that pulmonary leukocytes can be a significant source of proinflammatory cytokines, chemokines and replicating virus in both children and adults, however, the actual impetus for lung involvement in HIV infection is not known. Our previous studies suggest that both viral and nonviral conditions that lead to a heightened state of macrophage activation favor the replication of HIV in the lung. This, along with alterations in concentration gradients and patterns of cytokine expression that promote cellular activation, may be crucial for establishing this niche. Our previous studies have also indicated that latently infected CD4vT cells in the blood contribute only a portion of the viral rebound following cessation of combination antiretroviral therapy (ART) and that other sites appear to be the source of much of the rebounding virus. Pulmonary macrophages, which are relatively long-lived and for which HIV infection is not overtly cytopathic, have been suggested as a possible persistent reservoir of HIV replication, including during long periods of ART. Hence, the more long-term objectives of our proposal are to better define the relationship between host and viral factors that promote HIV replication in the lung, particularly during ART. To do this, we will examine the range of HIV-specific host cells in the lungs of HIV-positive persons in relation to the stage of disease and cytokine/chemokine expression profiles. This will be accomplished using ELISA and cDNA microarray technologies and by in situ hybridization techniques that allow for the localization and quantification of specific viral and cytokine mRNAs within phenotypically-defined cells obtained from induced sputum and bronchoalveolar lavage (BAL). With these data we will construct and evaluate mechanistic and nonmechanistic mathematical models for the interaction between cells that replicate HIV and those that express specific chemokine and proinflammatory cytokines in the lung. We hypothesize that persons with the highest concentrations of HIV RNA in lung tissues or sputum/BAL fluids will have more vRNA+ alveolar macrophages in tissues and fluids and these cells will produce more virus on a per-cell basis that persons with lower viral load. We also hypothesize that in such persons the pulmonary microenvironment will be altered in favor of a Thl -type cytokine milieu. Last, we will test the hypothesis that the lung is a separate virologic compartment from blood by examining titers and burst size of replicating virus and viral decay kinetics during ART. As such, we propose a central role for alveolar macrophages in the persistence of HIV replication and subsequent pathogenesis. In particular, we hypothesize that infection persists in these cells in an active state under ART to which we will assess by examining viral sequence diversity and divergence in treated vs. untreated persons.