1alpha,25-Dihydroxyvitamin d3 has a direct effect on naive CD4(+) T cells to enhance the development of Th2 cells

1alpha,25-Dihydroxyvitamin D3 (vitD3) is an immunoregulatory hormone with beneficial effects on Th1 mediated autoimmune diseases. Although the inhibitory effects of vitD3 on macrophages and dendritic cells are well documented, any direct effects of vitD3 on Th cell development are not clearly defined. Using CD4(+)Mel14(+) T cells derived from mice on a BALB/c and a C57BL/6 genetic background we examined the effect of vitD3 on Th cell development. We demonstrated that vitD3 affects Th cell polarization by inhibiting Th1 (IFN-gamma production) and augmenting Th2 cell development (IL-4, IL-5, and IL-10 production). These effects were observed in cultures driven with splenic APC and Ag, as well as with anti-CD3 and anti-CD28 alone, indicating that CD4(+) cells can also be direct targets for vitD3. The enhanced Th2 development by vitD3 was found in both BALB/c and C57BL/6 mice. An increased expression of the Th2-specific transcription factors GATA-3 and c-maf correlated with the increased production of Th2 cytokines after vitD3 treatment. The vitD3-induced effects were largely mediated via IL-4, because neutralization of IL-4 almost completely abrogated the augmented Th2 cell development after vitD3 treatment. These findings suggest that vitD3 acts directly on Th cells and can, in the absence of APC, enhance the development of a Th2 phenotype and augment the expression of the transcription factors c-maf and GATA-3. Our findings suggest that the beneficial effects of vitD3 in autoimmune diseases and transplantation operate through prevention of strong Th1 responses via the action on the APC, while simultaneously directly acting on the T cell to enhance Th2 cell development.

TGF-beta1 down-regulates Th2 development and results in decreased IL-4-induced STAT6 activation and GATA-3 expression

TGF-beta plays an important role in immune regulation in vivo and affects T cell differentiation in vitro. Here we describe how TGF-beta modulates Th2 development in vitro and investigate its mechanisms of action. TGF-beta down-regulated Th2 development of naive CD4+ Mel-14high T cells derived from the DO11.10 ovalbumin-specific TCR-transgenic mouse, and this was observed both in cultures driven with anti-CD3 and anti-CD28 and with splenic APC and antigen. TGF-beta down-regulated GATA-3 expression in developing Th2 and these cells showed a diminished IL-4-induced STAT6 activation. We found, however, that naive cells driven in Th2 conditions with TGF-beta did not show a significantly decreased STAT6 activation, suggesting that TGF-beta inhibits Th2 development via a STAT6-independent mechanism.

TGF-beta1 down-regulates Th2 development and results in decreased IL-4-induced STAT6 activation and GATA-3 expression

TGF-beta plays an important role in immune regulation in vivo and affects T cell differentiation in vitro. Here we describe how TGF-beta modulates Th2 development in vitro and investigate its mechanisms of action. TGF-beta down-regulated Th2 development of naive CD4+ Mel-14high T cells derived from the DO11.10 ovalbumin-specific TCR-transgenic mouse, and this was observed both in cultures driven with anti-CD3 and anti-CD28 and with splenic APC and antigen. TGF-beta down-regulated GATA-3 expression in developing Th2 and these cells showed a diminished IL-4-induced STAT6 activation. We found, however, that naive cells driven in Th2 conditions with TGF-beta did not show a significantly decreased STAT6 activation, suggesting that TGF-beta inhibits Th2 development via a STAT6-independent mechanism.

Cutting edge: ectopic expression of the IL-12 receptor-beta 2 in developing and committed Th2 cells does not affect the production of IL-4 or induce the production of IFN-gamma

The IL-12 receptor-beta 2 (IL-12R beta 2) chain is expressed on Th1 cells and lost upon differentiation to the Th2 phenotype. This has been suggested as the basis for commitment of Th1 cells, because early differentiated Th2 cells do not reverse their phenotype and do not produce IFN-gamma on restimulation in the presence of IL-12. In this study, we ectopically expressed the IL-12 receptor-beta 2 (IL-12R beta 2) bicistronically with enhanced green fluorescent protein by retroviral infection in developing and committed Th2 cells. Restimulation of Th2 cells expressing this ectopic IL-12R beta 2 in the presence of IL-12 led to levels of IL-4 production similar to those in control Th2 cells. The expression of IL-12R beta 2 in Th2 cells did not lead to significant levels of IFN-gamma production, although IL-12-mediated STAT signaling and proliferation were restored. Thus, although the IL-12R beta 2 and IL-12-dependent STAT4 activation are required for Th1 responses, activation of this pathway is not sufficient to restore a Th1 phenotype in developing or committed Th2 cells.

Peptides derived from murine insulin are diabetogenic in both rats and mice, but the disease-inducing epitopes are different: evidence against a common environmental cross-reactivity in the pathogenicity of type 1 diabetes

Two rodent models of autoimmune type 1 diabetes have been used to investigate the role of insulin as an autoantigen in this disease. In lymphopoenia-induced diabetes in the PVG.RT1u rat, neonatal tolerization with insulin B-chain peptides, but not A-chain peptides, conferred significant protection from disease. After rechallenge of adult rats, neonatally B-chain-tolerized animals showed diminished B-chain-specific T-cell proliferation, interleukin (IL)-2 production, and interferon-gamma (IFN-gamma) production, as compared with control animals. The epitope recognized by the PVG.RT1u rat was mapped to residues 1-18 of the B-chain; T-cell lines specific for this epitope were generated, and these conferred diabetes upon adoptive transfer to irradiated syngeneic recipients. In adult nonobese diabetic (NOD) mice, subcutaneous immunization with B-chain peptide 9-23 emulsified in incomplete Freund's adjuvant (IFA) was also potent at preventing onset of diabetes. In contrast to PVG.RT1u rats, NOD mice recognized an epitope within residues 10-29 of the insulin B-chain. The data implicate insulin as a target autoantigen in type 1 diabetes but do not support a role for molecular mimicry to insulin in the pathogenesis of this disease.

Intrathymic expression of genes involved in organ specific autoimmune disease

Insulin, thyroglobulin and myelin basic protein (MBP) are implicated as autoantigens in the autoimmune diseases, insulin-dependent diabetes mellitus (IDDM), autoimmune thyroid-disease and multiple sclerosis. Self tolerance to these antigens, until recently only thought to be present extrathymically, is generally considered to be maintained by 'peripheral' mechanisms, such as clonal anergy or clonal ignorance. The techniques of reverse transcription and polymerase chain reaction (RT-PCR) were used to investigate the intrathymic expression of these genes. Expression was examined in mRNA isolated from complete adult rat thymus, various mouse thymic cell-types isolated from fetal thymic-organ cultures and from neonatal-mouse thymocyte subsets. mRNA for insulin, thyroglobulin and MBP were detected in unfractionated adult rat and embryonic mouse thymus. Rat thymus expressed both insulin I and II, while mouse thymus only expressed insulin II. Thyroglobulin and MBP, but not insulin mRNA were detected in mouse MHC class II+ thymic epthelial cells and class II+ dendritic cells and in certain thymocyte subsets. The presence of insulin, thyroglobubin and MBP mRNA in the thymus has important implications for the development of the T-cell repertoire, particularly for the mechanisms of tolerance that prevent autoreactivity to these antigens in healthy individuals.

The role of the thymus in the control of autoimmunity

Self tolerance among T cells is believed to be maintained by two principal mechanisms: clonal deletion for self antigens expressed in the thymus and T cell anergy or T cell indifference for those whose expression is solely extrathymic. These mechanisms are passive in that they depend on autoreactive T cells being either eliminated during their maturation or rendered intrinsically non-responsive after they have matured. The data presented in this paper indicate that this scheme requires modification. First, it is evident that self antigens that are commonly regarded as being tissue-specific may also be expressed in the thymus where they influence the developing T cell repertoire. Second, it appears that there is some T cell-mediated regulatory mechanism that actively prevents potentially autoreactive T cells from expressing their disease-inducing potential. Our data indicate that this regulatory mechanism is established intrathymically and is an innate property of the naive T cell repertoire. The mechanism is discussed in terms of what is currently known of the ways that an individual T cell responds when interacting with agonist and antagonist peptides and possible therapeutic implications are considered.