Many antigen-specific T cells die after exposure to antigen in animals. These cells also die if they are isolated from animals shortly after activation and cultured. Various cytokines were tested for their ability to interfere with this in vitro death. Surprisingly, tumor necrosis factor ␣ and other inf lammatory cytokines did not prevent the in vitro death of activated T cells, even though these cytokines do prevent activated T cell death in animals. Therefore, the inf lammatory cytokines probably act on T cells in vivo via an intermediary factor.

The B cell antigen receptor complex is a hetero-oligomeric structure composed of antigen binding, membrane immunoglobulin, and transducer-transporter substructures. The transducer-transporter substructure is composed of disulfide-linked dimers of immunoglobulin (Ig)-alpha and Ig-beta/gamma subunits that are products of the mb-1(alpha) and B29 (beta/gamma) genes. Although the receptor complex associates with Src family kinases that are activated after receptor ligation, the site of interaction of these and other cytoplasmic effector molecules with receptor subunits is unknown. The cytoplasmic tails of Ig-alpha and Ig-beta chains were found to associate with distinct sets of effector molecules. The Ig-alpha chain cytoplasmic domain bound to the Src family kinases Lyn and Fyn, phosphatidylinositol-3 kinase (PI-3 kinase), and an unidentified 38-kilodalton phosphoprotein; the cytoplasmic tail of Ig-beta bound PI-3 kinase and unidentified 40- and 42-kilodalton phosphoproteins. Binding activity was found to occur within a 26-amino acid sequence of Ig-alpha and Ig-beta that contains a motif [(Asp or Glu)-(any amino acid)7-(Asp or Glu)-Tyr-(any amino acid)3-Leu-(any amino acid)7-Tyr-(any amino acid)2-(Leu or Ile)] previously implicated in signal transduction via other receptors including the Fc epsilon receptor I and the T cell antigen receptor. These findings indicate that the subunits act independently to activate distinct second messenger pathways.

SummaryTo study the role ofCD8 + T cells in allergic sensitization, we examined the effects of in vivo depletion ofCD8 + T cells prior to sensitization on IgE production, immediate type cutaneous hypersensitivity and development of altered airway responsiveness. BALB/c mice were thymectomized and treated with anti-CD8 antibody resulting in depletion of CD8 + T cells (< 1%) in spleen and lymphoid tissues. In these mice, sensitization to ovalbumin (OVA) via the airways still resulted in IgE anti-OVA responses and immediate cutaneous reactions to OVA, but the animals were unable to develop airway hyperresponsiveness, eosinophil infiltration of the lung parenchyma, or IL-5 production in the local lymph nodes of the airway. Transfer of CD8 + T cells from naive animals during sensitization (on day 8 of the 10-d protocol) fully restored the ability to develop airway hyperresponsiveness and this was accompanied by IL-5 production and eosinophil accumulation in the lung. These data indicate a critical role for CD8 + T cells in the production of IL-5 and the development of altered airway responsiveness after antigen sensitization through the airways.