T cell activation plays a major role in the ability of the HIV to remain latent or establish a productive infection. The alpha-chain of the IL-2R (CD25, Tac, p55) is expressed on activated but not resting T cells and therefore represents an ideal marker to distinguish activated from resting T cells. The present studies were designed to define the role of CD25+ (activated) and CD25- (resting) T cells in an acute HIV infection in vitro. This objective was accomplished by selectively killing CD25+ cells with an anti-CD25-ricin A chain immunotoxin (RFT5-deglycosylated ricin A (dgA)) either before or after HIV infection, and then determining the effect of eliminating these cells on the secretion of viral p24 Ag. Three major findings have emerged from this study: 1) Elimination of the small population (3 to 5%) of activated, CD25+ cells present in normal PBMC before HIV infection results in a 99% reduction in p24 secretion. 2) RFT5-dgA, an immunotoxin directed against CD25, kills HIV-infected CD25+ cells. Elimination of the CD25+ cells after infection with HIV virtually stops viral production and the spread of the infection in these cultures. This was confirmed by coculturing RFT5-dgA-treated PBMC with H9 cells. 3) When RFT5-dgA-treated PBMC (CD25-cells) were infected with HIV and then activated with a solid phase anti-CD3 mAb, the levels of p24 produced were comparable with those of PBMC from which the CD25+ cells had not been eliminated. Taken together these findings suggest that both activated (CD25+) and resting/quiescent (CD25-) cells can be infected with HIV but that only the CD25+ cells produce viral proteins in the absence of additional activation.

No abstract

Small, resting, surface IgM+/surface IgD+ murine B cells undergo an Ig class switch to IgG1 or IgE after stimulation with LPS and T cell supernatants containing IL-4. To firmly establish the role of IL-4 in the directed switch recombination observed in IgG1-secreting cells, we have 1) used highly purified native IL-4 instead of T cell supernatants, 2) used resting B cells from F1 mice in which the active IgH allele was determined before culture, 3) taken advantage of the allelic differences in the restriction fragment lengths of mu, gamma 1, gamma 2b, and gamma 3 loci to determine the status of the CH genes on both the expressed and unexpressed chromosomes, and 4) used different restriction enzymes to distinguish between deletion and rearrangement of a given CH gene. Our results indicate that LPS alone induces rearrangement of the gamma 3 genes on both chromosomes whereas stimulation with LPS plus IL-4 results in deletion of gamma 3 genes and rearrangement of gamma 1 genes on both chromosomes. The studies definitively establish the role of IL-4 in directed switch recombination to the gamma 1 locus in LPS-stimulated murine B cells.

Concanavalin A induced polyclonal antibody synthesis in normal spleen cells in vitro. Optimal responses were obtained by Con A concentrations lower than those optimal for induction of DNA synthesis. T cells, but not macrophages, were necessary for the effect. Spleen cells from nude mice were not activated, whereas cells from the LPS non-responder stain C3H/HeJ were activated to polyclonal antibody synthesis by Con A. Supernatants from Con A activated spleen cells could by themselves induce polyclonal antibody synthesis in untreated spleen cell cultures, even when Con A had been removed by absorption with Sephadex G-50 and when alpha-methyl-mannoside was present in the secondary cultures. T cells produced the active supernatants, which were competent to induce polyclonal antibody synthesis, but not DNA synthesis, in both H-2-incompatible and compatible strains. When the supernants were absorbed with erythrocyte antigens, they specifically induced an enhanced response, in secondary cultures, to the antigen used for absorption. Possible mechanisms of this specific effect are discussed.

The role of alveolar macrophages (M phi) in the induction of immune responses within the lung was investigated. Guinea pig alveolar M phi obtained from bronchoalveolar cells (BAC) were found to function as well as peritoneal exudate M phi in supporting proliferation of purified lymph node lymphocytes (LNL) induced by both soluble antigens and mitogen (Con A). Several lines of evidence indicate that the alveolar M phi is an effective antigen-presenting cell. 1) Washed alveolar M phi, previously "pulsed" with antigen, replaced both soluble antigen and BAC in the stimulation of immune LNL. 2) The interaction of alveolar M phi, over 80% of which were Ia positive, with lymphocytes was genetically restricted, i.e., only antigen-pulsed alveolar M phi that shared I region-encoded antigens with the antigen-specific T lymphocytes stimulated their proliferation. Furthermore, removal of Ia-positive alveolar M phi abrogated this response. 3) Antigen-pulsed alveolar M phi specifically bound immune T lymphocytes. In contrast, no evidence was obtained for immunosuppression by alveolar M phi. Thus, alveolar M phi failed to suppress specific LNL proliferation even at ratios of alveolar M phi to LNL of greater than 20:1, ratios that often exist locally within the lung. The possible role of antigen-bearing alveolar M phi in inducing local immunity and also in focusing a systemic response are discussed.