CD28/CTLA4 double deficient mice demonstrate crucial role for B7 co-stimulation in the induction of allergic lower airways disease

Background The existence of a third B7-1/B7-2 receptor was postulated in a recent study using a novel mouse strain lacking both CD28 and CTLA4 (CD28/CTLA4(-/-)).Objective In the present study, it was investigated if T cell co-stimulation via the putative B7-1/B7-2 receptor plays a role in the induction of Th2-mediated asthma manifestations in mice.Methods BALB/c wild-type, CD28/CTLA4(-/-) and B7-1/B7-2(-/-) mice were sensitized and aerosol challenged with ovalbumin (OVA).Results At 24 h after the last aerosol, wild-type mice showed airway hyper-responsiveness in vivo and up-regulated levels of serum OVA-specific IgE compared with the situation shortly before OVA challenge. In addition, eosinophil numbers and IL-5 levels in the broncho-alveolar lavage fluid and Th2 cytokine production by lung cells upon OVA re-stimulation in vitro were observed. In agreement with an earlier study, we failed to induce any of the asthma manifestations in B7-1/B7-2(-/-) mice. Importantly, also CD28/CTLA4(-/-) mice showed no asthma manifestations upon OVA sensitization and challenge.Conclusion These data clearly demonstrate that T cell co-stimulation via the putative B7-1/B7-2 receptor appears to have no role in the induction of Th2-mediated asthma manifestations in this murine model and, conversely, that CD28 signalling is crucial.</p

Instruction of naive CD4+ T-cell fate to T-bet expression and T helper 1 development: roles of T-cell receptor-mediated signals

Using T-cell receptor (TCR) transgenic mice, we demonstrate that TCR stimulation of naive CD4+ T cells induces transient T-bet expression, interleukin (IL)-12 receptor β2 up-regulation, and GATA-3 down-regulation, which leads to T helper (Th)1 differentiation even when the cells are stimulated with peptide-loaded I-Ab-transfected Chinese hamster ovary cells in the absence of interferon-γ (IFN-γ) and IL-12. Sustained IFN-γ and IL-12 stimulation augments naive T-cell differentiation into Th1 cells. Intriguingly, a significant Th1 response is observed even when T-bet–/– naive CD4+ T cells are stimulated through TCR in the absence of IFN-γ or IL-12. Stimulation of naive CD4+ T cells in the absence of IFN-γ or IL-12 with altered peptide ligand, whose avidity to the TCR is lower than that of original peptide, fails to up-regulate transient T-bet expression, sustains GATA-3 expression, and induces differentiation into Th2 cells. These results support the notion that direct interaction between TCR and peptide-loaded antigen-presenting cells, even in the absence of T-bet expression and costimulatory signals, primarily determine the fate of naive CD4+ T cells to Th1 cells

CTLA-4 regulates allergen response by modulating GATA-3 protein level per cell

T helper type 2 (Th2) cell differentiation requires the expression of GATA-3, a transcription factor that allows transcriptional activation of Th2 cytokine genes through chromatin remodelling. We investigated the role of the negative costimulatory receptor cytotoxic T-lymphocyte antigen 4 (CTLA-4) in the regulation of GATA-3 expression, Th2 differentiation and immunoglobulin production during the immune response to allergens. BALB/c mice were immunized with a recombinant major allergenic component of Parietaria judaica pollen, rPar j I, and treated with blocking anti-CTLA-4 or control antibodies. Results showed that in vivo CTLA-4 blockade enhanced the Par j I-specific immunoglobulin E (IgE) serum level. In contrast, Par j I-specific IgG2a serum level was reduced, suggesting that CTLA-4 blockade skewed immunoglobulin production towards interleukin-4 (IL-4) -dependent immunoglobulin isotypes. Consistently, CTLA-4 blockade increased the frequency of Par j I-specific Th2 cells but not Th1 cells, as well as IL-4 and IL-5 but not interferon-γ production. Our data also showed that CTLA-4 blockade enhanced the GATA-3 : T-bet messenger RNA ratio. Interestingly, in vivo CTLA-4 blockade did not increase the frequency of GATA-3 protein-expressing cells. In contrast, it enhances GATA-3 protein level per cell. Further, in vitro results show that the anti-CTLA-4 monoclonal antibody, by competing with CD80 for CTLA-4 binding, induced an enhancement in the frequency of IL-4-producing cells that correlates with the increase in GATA-3 protein level per cell. In conclusion, CTLA-4, by affecting the level of GATA-3 per cell, contributes to keeping this factor under the threshold required to become a Th2 effector cell. Consequently, it affects IgE/IgG2a production and contributes to the outcome of allergen-specific immune responses