NF-kappaB is involved in regulation of CD40 ligand expression on Mycobacterium bovis bacillus Calmette-Guérin-activated human T cells

An IgD-Fc-Ig fusion protein restrains the activation of T and B cells by inhibiting IgD-IgDR-Lck signaling in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by synovitis and the destruction of small joints. Emerging evidence shows that immunoglobulin D (IgD) stimulation induces T-cell activation, which may contribute to diseases pathogenesis in RA. In this study, we investigated the downstream signaling pathways by which IgD activated T cells as well as the possible role of IgD in the T-B interaction. Peripheral blood mononuclear cells were isolated from peripheral blood of healthy controls and RA patients. We demonstrated that IgD activated T cells through IgD receptor (IgDR)-lymphocyte-specific protein tyrosine kinase (Lck)-zeta-associated protein 70 (ZAP70)/phosphatidylinositol 3-kinase (PI3K)/nuclear factor kappa-B (NF-κB) signaling pathways; IgD-induced CD4⁺ T cells promoted the proliferation of CD19⁺ B cells in RA patients. A novel fusion protein IgD-Fc-Ig (composed of human IgD-Fc domain and IgG₁ Fc domain, which specifically blocked the IgD-IgDR binding) inhibited the coexpression of IgDR and phosphorylated Lck (p-Lck) and the expression levels of p-Lck, p-ZAP70, p-PI3K on CD4⁺ T cells, and decreased NF-κB nuclear translocation in Jurkat cells. Meanwhile, IgD-Fc-Ig downregulated the expression levels of CD40L on CD4⁺ T cells as well as CD40, CD86 on CD19⁺ B cells in RA patients and healthy controls. It also decreased the expression levels of CD40L on CD4⁺ T cells and CD40 on CD19⁺ B cells from spleens of collagen-induced arthritis (CIA) mice and reduced IL-17A level in mouse serum. Moreover, administration of IgD-Fc-Ig (1.625-13 mg/kg, iv, twice a week for 4 weeks) in CIA mice dose-dependently decreased the protein expression levels of CD40, CD40L, and IgD in spleens. IgD-Fc-Ig restrains T-cell activation through inhibiting IgD-IgDR-Lck-ZAP70-PI3K-NF-κB signaling, thus inhibiting B-cell activation. Our data provide experimental evidences for application of IgD-Fc-Ig as a highly selective T cell-targeting treatment for RA.

Impaired NFAT and NFκB activation are involved in suppression of CD40 ligand expression by Δ(9)-tetrahydrocannabinol in human CD4(+) T cells

We have previously reported that Δ(9)-tetrahydrocannabinol (Δ(9)-THC), the main psychoactive cannabinoid in marijuana, suppresses CD40 ligand (CD40L) expression by activated mouse CD4(+) T cells. CD40L is involved in pathogenesis of many autoimmune and inflammatory diseases. In the present study, we investigated the molecular mechanism of Δ(9)-THC-mediated suppression of CD40L expression using peripheral blood human T cells. Pretreatment with Δ(9)-THC attenuated CD40L expression in human CD4(+) T cells activated by anti-CD3/CD28 at both the protein and mRNA level, as determined by flow cytometry and quantitative real-time PCR, respectively. Electrophoretic mobility shift assays revealed that Δ(9)-THC suppressed the DNA-binding activity of both NFAT and NFκB to their respective response elements within the CD40L promoter. An assessment of the effect of Δ(9)-THC on proximal T cell-receptor (TCR) signaling induced by anti-CD3/CD28 showed significant impairment in the rise of intracellular calcium, but no significant effect on the phosphorylation of ZAP70, PLCγ1/2, Akt, and GSK3β. Collectively, these findings identify perturbation of the calcium-NFAT and NFκB signaling cascade as a key mechanistic event by which Δ(9)-THC suppresses human T cell function.

The effect of age on the cognate function of CD4+ T cells

With increasing age, the ability to produce protective antibodies in response to immunization declines, resulting in reduced efficacy of vaccination. We have examined how reductions in CD4(+) T-cell function contribute to reduced humoral responses, using a model that allows us to compare identical numbers of antigen-specific naive T cells from young and aged T-cell receptor transgenic mice. Naive cells from aged mice exhibit reduced responses, both in vitro and in vivo. In vitro, responses of aged T cells can be enhanced by addition of interleukin (IL)-2. In vivo, using an adoptive transfer model with young hosts, naive cells from aged mice exhibit significant reductions in cognate helper function, leading to reduced B-cell expansion and differentiation. These age-related defects could be overcome by prior in vitro T helper 2 effector generation with aged T cells. This improvement in cognate function of the aged effectors may be related to the enhancement of CD154 expression, which occurs on aged T cells in the presence of exogenous IL-2. We also found no difference in B-cell expansion and differentiation when young cells were transferred to young or aged hosts. Our results indicate that age-related reductions in humoral responses are mainly due to defects in the cognate helper function of naive CD4(+) T cells from aged individuals.

Age-related defects in CD4 T cell cognate helper function lead to reductions in humoral responses

With increasing age, the ability to produce protective antibodies in response to immunization declines, leading to a reduced efficacy of vaccination in the elderly. To examine the effect of age on the cognate function of CD4 T cells, we have used a novel adoptive transfer model that allows us to compare identical numbers of antigen-specific naive T cells from young and aged TCR transgenic (Tg) donors. Upon transfer of aged donor CD4 T cells to young hosts, there was significantly reduced expansion and germinal center (GC) differentiation of the antigen-specific B cell population after immunization. This reduced cognate helper function was seen at all time points and over a wide range of donor cell numbers. In hosts receiving aged CD4 cells, there were also dramatically lower levels of antigen-specific IgG. These age-related defects were not due to defects in migration of the aged CD4 T cells, but may be attributable to reduced CD154 (CD40L) expression. Furthermore, we found that there was no difference in B cell expansion and differentiation or in IgG production when young CD4 T cells were transferred to young or aged hosts. Our results show that, in this model, age-related reductions in the cognate helper function of CD4 T cells contribute significantly to defects in humoral responses observed in aged individuals.