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.

The mechanisms underlying the development of airway hyperresponsiveness are not fully delineated. We addressed this question by studying the effects of passive sensitization with anti-OVA IgE on the development of altered airway responsiveness (AR) following local challenge with OVA in normal and athymic mice. Both normal and athymic BALB/c mice developed allergen-specific immediate cutaneous hypersensitivity after passive sensitization with anti-OVA IgE. In contrast, the combination of local challenge with allergen via the airways and passive sensitization triggered the development of airway hyperresponsiveness only in normal but not in athymic mice. Treatment of athymic mice with IL-5 significantly increased eosinophil accumulation in the lungs after local challenge with OVA; increased airway reactivity was only observed in athymic mice which received anti-OVA IgE, not an unrelated IgE, plus IL-5 treatment and airway challenge with OVA. These findings identify the requirement for allergen-specific IgE and IL-5 for the development of airway hyperresponsiveness following allergen challenge via the airways.

The role of allergen-specific sIgE+ B cells in the development of airway hyperresponsiveness to electrical field stimulation was examined in a murine model of allergic sensitization. Ovalbumin (OVA)-specific B cells (OVA+) were isolated from mice that were sensitized to aerosolized OVA. The OVA+ B cell population was shown to be distinct from the remaining, non-OVA-responsive B cells (OVA-). There was a high frequency of sIgE+ B cells and a low frequency of sIgG+ B cells in the OVA+ population compared with the OVA- population, where the ratio was reversed. Although both populations produced immunoglobulin in vitro, only the OVA+ cells secreted anti-OVA antibodies. Transfer of 10(6) OVA+ B cells or as few as 5 x 10(4) OVA+/sIgE+ B cells was able to transfer the capability for anti-OVA IgE synthesis and cutaneous reactivity to OVA in naive recipients. Exposure to OVA via the airways in addition to transfer of OVA+ B cells was necessary for development of airway hyperresponsiveness, whereas recipients challenged with an irrelevant allergen, ragweed, had normal airway function. Transfer of up to 10(7) OVA- B cells failed to induce production of anti-OVA IgE. Despite production of polyclonal IgE, recipients of OVA- B cells did not develop airway hyperresponsiveness after OVA challenge. We conclude that both allergen-specific IgE production and local challenge via the airways with specific allergen are necessary to change airway function in this model.

Sensitization of BALB/c mice to ovalbumin (OVA) through the airways stimulated allergen-specific immediate hypersensitivity responses and these effects were related to the expansion of V beta 8.1/8.2+ T cells. In contrast, splenic V beta 2+ T cells from sensitized animals inhibited V beta 8.1/8.2+ T-cell induction of anti-OVA IgE production in vivo. To examine whether such differences in T-cell function were associated with differences in cytokine production, CD4+ T cells and CD4+ T cells depleted of V beta 8.1/8.2+ T cells were analyzed for interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) production. In nonsensitized animals, no differences in IL-4 and IFN-gamma production were found in mRNA levels as well as in protein levels in these two populations of cells. In contrast, CD4+ T cells from sensitized mice showed higher IL-4 and lower IFN-gamma production than CD4+ cells depleted of V beta 8+ lymphocytes. Similar results were obtained after stimulation of CD4+ T cells from OVA-sensitized animals with anti-V beta 2 and anti-V beta 8.1/8.2 antibodies. Stimulation of V beta 8.1/8.2+ T cells from sensitized mice with OVA or OVA peptide 323-339 also resulted in increased production of IL-4. These data indicate that allergen sensitization via the airways stimulates the selective expansion of certain V beta-expressing T cells and that these T-cell subsets exhibit different functional activities in terms of cytokine production.