Hyper immunoglobulin E response in mice with monoclonal populations of B and T lymphocytes

A key event in the pathogenesis of allergies is the production of antibodies of the immunoglobulin (Ig)E class. In normal individuals the levels of IgE are tightly regulated, as illustrated by the low serum IgE concentration. In addition, multiple immunizations are usually required to generate detectable IgE responses in normal experimental animals. To define the parameters that regulate IgE production in vivo, we generated mice bearing monoclonal populations of B and T lymphocytes specific for influenza virus hemagglutinin (HA) and chicken ovalbumin (OVA), respectively. A single immunization of the monoclonal mice with the cross-linked OVA-HA antigen led to serum IgE levels that reached 30-200 microg/ml. This unusually high IgE response was prevented by the infusion of regulatory alpha/beta CD4(+) T cells belonging to both CD25(+) and CD25(-) subpopulations. The regulation by the infused T cells impeded the development of fully competent OVA-specific effector/memory Th2 lymphocytes without inhibiting the initial proliferative response of T cells or promoting activation-induced cell death. Our results indicate that hyper IgE responses do not occur in normal individuals due to the presence of regulatory T cells, and imply that the induction of regulatory CD4(+) T cells could be used for the prevention of atopy.

Expression of bcl-X(L) restores cell survival, but not proliferation off effector differentiation, in CD28-deficient T lymphocytes

Lymphocytes deficient in the T cell costimulatory molecule CD28 exhibit defects in cell survival, clonal expansion, and differentiation into effector cells. It is known that CD28-mediated signaling results in the upregulation of the Bcl family member Bcl-X(L). To investigate the role that Bcl-X(L) plays in the various functions of CD28, we expressed Bcl-X(L) in CD28-deficient primary T lymphocytes using retrovirus-mediated gene transfer. T cells were activated in vitro and infected with Bcl-X(L) or control retroviruses; this method allows gene expression in activated, cycling cells. Expression of Bcl-X(L) in naive T cells was achieved by reconstitution of the immune system of lethally irradiated recipient mice with retrovirus-infected purified bone marrow stem cells from CD28(-/)- or wild-type donor mice. Our studies demonstrate that Bcl-X(L) prolongs the survival of CD28(-/)- T cells but does not restore normal proliferation or effector cell development. These results indicate that the various functions of CD28 can be dissociated, and provide an experimental approach for testing the roles of downstream signals in the functions of cellular receptors such as CD28.

Antigen-specific signaling by a soluble, dimeric peptide/major histocompatibility complex class II/Fc chimera leading to T helper cell type 2 differentiation

Interaction between a T cell receptor (TCR) and various ligands, i.e. , anti-TCR antibodies, superantigens, peptides, or altered peptide ligands in the context of major histocompatibility complex (MHC) molecules can trigger different T helper cell (Th) effector functions. Herein, we studied the T cell response induced by a soluble, dimeric peptide/MHC class II chimera, namely hemagglutinin (HA)110-120/I-E(d)alphabeta/Fcgamma2a (DEF). We have previously demonstrated that the soluble DEF molecule binds stably and specifically to HA110-120-specific TCRs expressed by a T cell hybridoma. Administration of DEF in vivo induced differentiation of resting and activated peptide-specific T cells toward a Th2 response, as indicated by the increase of interleukin (IL)-4, IL-10, and specific immunoglobulin (Ig)G1 antibodies and decrease of IL-2, specific IgG2a antibodies, and cytotoxic T lymphocyte activity. In contrast to HA110-120 peptide presented by the DEF molecule to T cells, the nominal synthetic peptide induced a predominant Th1 response, and the PR8 virus-derived HA110-120 peptides induced a mixed Th1/Th2 response. Independent of antigen processing, soluble DEF was almost 2 logs more potent in stimulating cognate T cells than the nominal peptide. Polarization of cognate T cells toward the Th2 response occurred upon interaction of soluble DEF with TCR and CD4 molecules followed by early activation of p56(lck) and ZAP-70 tyrosine kinases, and negative signaling of the signal transducer and activator of transcription (STAT)4 pathway of Th1 differentiation. DEF-like molecules may provide a new tool to study the mechanisms of signaling toward Th2 differentiation and may also provide a potential immunotherapeutic approach to modulate autoreactive T cells toward protective Th2 immune responses.