In this study we examined the immunological parameters underlying the natural immunity to inhaled nonpathogenic proteins. We addressed this question by examining the effect of intranasal exposure to OVA in both wild-type mice and mice reconstituted with OVA-TCR transgenic CD4+ T cells. Intranasal administration of OVA induced an initial phase of activation during which CD4+ T cells were capable of proliferating and producing cytokines. Although many of the OVA-specific CD4+ T cells were subsequently depleted from the lymphoid organs, a stable population of such T cells survived but remained refractory to antigenic rechallenge. The unresponsive state was not associated with immune deviation due to selective secretion of Th1- or Th2-type cytokines, and the presence of regulatory CD8+ T cells was not required. Moreover, neutralization of the immunosuppressive cytokines IL-10 and TGF-beta did not abrogate the induction of tolerance. Inhibition of the interaction of T cells with CD86, but not CD80, at the time of exposure to intranasal Ag prevented the development of unresponsiveness, while selective blockade of CTLA-4 had no effect. Our results suggest that intranasal exposure to Ags results in immunological tolerance mediated by functionally impaired CD4+ T cells via a costimulatory pathway that requires CD86.

We used an adoptive transfer system and CD4+ T cell clones with defined lymphokine profiles to examine the role of CD4+ T cells and the types of lymphokines involved in the development of B cell memory and affinity maturation. Keyhole limpet hemocyanin (KLH)-specific CD4+ Th2 clones (which produce IL-4 and IL-5 but not IL-2 or IFN-gamma) were capable of inducing B cell memory and affinity maturation, after transfer into nude mice or after transfer with unprimed B cells into irradiated recipients and immunization with TNP-KLH. In addition, KLH-specific Th1 clones, which produce IL-2 and IFN-gamma but not IL-4 or IL-5, were also effective in inducing B cell memory and high affinity anti-TNP-specific antibody. The induction of affinity maturation by Th1 clones occurred in the absence of IL-4, as anti-IL-4 mAb had no effect on the affinity of the response whereas anti-IFN-gamma mAb completely blocked the response. Th1 clones induced predominantly IgG2a and IgG3 antibody, although Th2 clones induced predominantly IgG1 and IgE antibody. We thus demonstrated that some Th1 as well as some Th2 clones can function in vivo to induce Ig synthesis. These results also suggest that a single type of T cell with a restricted lymphokine profile can induce both the terminal differentiation of B cells into antibody secreting cells as well as induce B cell memory and affinity maturation. Moreover, these results suggest that B cell memory and affinity maturation can occur either in the presence of Th2 clones secreting IL-4 but not IFN-gamma, or alternatively in the presence of Th1 clones secreting IFN-gamma but not IL-4.

Strains of mice differ greatly in their capacity to produce interleukin (IL) 4 and high levels of serum IgE. The contribution of macrophages (M-PHI) in enhancing the production of IL 4 by T cells in high-IgE responder mice was studied. M-PHI from BALB/c mice (high-IgE responder strain) developed an augmented capacity to present antigen to IL 4-producing T helper type 2 (T(h)2) clones, when the M-PHI were pretreated by exposure to the lymphokines IL 4 and IL 5. In contrast, identical treatment of M-PHI from H-2-identical DBA/2 mice (low-IgE responder strain) resulted in inhibition of the capacity to stimulate T(h)2 clones. The impairment of antigen presentation by DBA/2 M-PHI was closely paralleled by a decrease of cell surface class II major histocompatibility complex (MHC) expression and an abrogation of IL 1 production by these cells, while identical treatment of BALB/c M-PHI enhanced class II MHC expression and did not inhibit secretion of IL 1. Our studies demonstrate that IL 4 and IL 5 can exert different effects on M-PHI from high- and low-IgE responder strains of mice, resulting in down-regulation of the expansion of IL 4-producing cells in low- but not high-IgE responder mice.

The synthetic random copolymer of L-glutamic acid and L-lysine (GL) is weakly or nonimmunogenic in all inbred strains of mice. Theories proposed to account for nonresponsiveness to GL include a deficient T cell repertoire, failure of antigen-presenting cells to present the antigen and/or the presence of suppressor cells. In this study we examine mechanisms for nonresponsiveness to GL. We demonstrate the existence of GL-reactive T cells which can be isolated with a relatively high frequency. These clones, which were derived following immunization of H-2d mice with poly(LGluLLysLTyr), also respond to several GL-containing polypeptides including the terpolymers of GL with phenylalanine, alanine (GLA) or leucine. Although recognition of GLA by heterogeneous T cell populations usually occurs in association with I-A determinants, these clones recognize GLA, as well as the other GL-containing polymers, in association with I-E determinants. Analysis of the antigen and alloreactivity patterns of these clones indicated that they expressed distinct antigen receptors. These studies imply that the T cell repertoire of "nonresponder" H-2d mice includes multiple GL-reactive T cell clones and that the antigen-presenting cells of these mice are effective in processing and presenting GL.

To gain insight into the nature of the syngeneic T cell-stimulating molecules on SJL lymphoma cells (RCS), a panel of eight Ly-1+2- T cell clones that are specific for transplantable RCS has been generated. All of these clones proliferate vigorously in response to two independent RCS lines and to LPS-activated syngeneic or F1 B cell blasts, but not to unstimulated SJL spleen cells or to allogeneic B cell blasts. Only one RCS-specific clone displays a proliferative response to (SJL X BALB/c) resting spleen cells, suggesting that I-E molecules are not the source of stimulation of RCS-responsive cells. Responses of the T cell clones to both RCS and syngeneic LPS-activated B cells are inhibited by monoclonal antibodies to I-A antigens, and not by antibody to I-E antigens. These findings suggest that RCS-responsive T cells are stimulated either by syngeneic I-As alone, in a form expressed on activated B cells, or by I-As in combination with X, where X is a cell surface antigen present on B cells at certain stages of differentiation.