Treatment of alveolar epithelial monolayers from wild type rats with either gp120 or Tat for 24 hrs altered expression of occludin and ZO-1. Treatment with either gp120 or Tat significantly decreased (P < 0.05) the gene expression of occludin and Tat when compared to untreated control cells (Panel A). Although occludin and ZO-1 protein expression were either unchanged or increased (* P < 0.05) in the cytosol (Triton X-100 soluble) fractions (Panel B, left side) following these short-term exposures, Tat treatment significantly decreased (*P < 0.05) both occludin and ZO-1 protein expression in the membrane/cytoskeleton (Triton X-100 insoluble) fractions (panel B, right side). In parallel, and consistent with the images shown in Figure 4, treatment with either gp120 or Tat altered the membrane localization of occludin and ZO-1. Shown in panels C and D are representative fluorescent immunocytochemistry images illustrating that the relative distribution of ZO-1 (Panel C) and occludin (Panel D) was less uniform in the plasma membranes of gp120-treated or Tat-treated alveolar epithelial monolayers compared to untreated (control) monolayers, with more granular staining for each protein within the cytoplasm of the cells. The magnification bar in the lower right image of each panel = 100 microns.