T-cell receptor antagonist modifies cytokine secretion profile of naive CD4+ T cells and their differentiation into type-1 and type-2 helper T cells

Isatis root polysaccharide promotes maturation and secretory function of monocyte-derived dendritic cells

Background

Pseudorabies virus (PRV) is an animal virus that is globally responsible for the high economic losses in the swine industry. Isatis root is a traditional Chinese medicinal herb that possesses immune-enhancing and antiviral properties. However, the molecular mechanisms underlying the effects of the active component of the isatis root polysaccharide (IRPS) extract on immature dendritic cells remain elusive.

Methods

In this study, we investigated the molecular changes in primary porcine peripheral blood monocyte-derived dendritic cells (MoDCs) during PRV infection, using enzyme-linked immunosorbent assay (ELISA) and quantitative reverse transcription-polymerase chain reaction. Additionally, we studied the effect of IRPS on PRV-infected DCs.

Results

The results showed that IRPS stimulated the maturation of MoDCs, induced IL-12 secretion, and downregulated IL-6 expression.

Conclusions

Collectively, these results suggest that IRPS is a promising candidate for promoting maturation of DCs and enhancing their secretory potential after PRV infection.

Predominant clonal accumulation of CD8+ T cells with moderate avidity in the central nervous systems of Theiler's virus-infected C57BL/6 mice

Induction of antigen-specific CD8(+) T cells bearing a high-avidity T-cell receptor (TCR) is thought to be an important factor in antiviral and antitumor immune responses. However, the relationship between TCR diversity and functional avidity of epitope-specific CD8(+) T cells accumulating in the central nervous system (CNS) during viral infection is unknown. Hence, analysis of T-cell diversity at the clonal level is important to understand the fate and function of virus-specific CD8(+) T cells. In this study, we examined the Vbeta diversity and avidity of CD8(+) T cells specific to the predominant epitope (VP2(121-130)) of Theiler's murine encephalomyelitis virus. We found that Vbeta6(+) CD8(+) T cells, associated with epitope specificity, predominantly expanded in the CNS during viral infection. Further investigations of antigen-specific Vbeta6(+) CD8(+) T cells by CDR3 spectratyping and sequencing indicated that distinct T-cell clonotypes are preferentially increased in the CNS compared to the periphery. Among the epitope-specific Vbeta6(+) CD8(+) T cells, MGX-Jbeta1.1 motif-bearing cells, which could be found at a high precursor frequency in naïve mice, were expanded in the CNS and tightly associated with gamma interferon production. These T cells displayed moderate avidity for the cognate epitope rather than the high avidity normally observed in memory/effector T cells. Therefore, our findings provide new insights into the CD8(+) T-cell repertoire during immune responses to viral infection in the CNS.

A unique unresponsive CD4+ T cell phenotype post TCR antagonism

The functional outcomes of the T cell's interaction with the peptide:MHC complex can be dramatically altered by the introduction of a single amino acid substitution. Previous studies have described the varied effects of these altered peptide ligands (APL) on T cell responses. These outcomes of T cell interaction with an APL include the induction of clonal unresponsiveness (anergy) and inhibition of T cell responses (antagonism). The phenotype of peptide-induced anergy, i.e. low proliferation and low IL-2 production, has been extensively described, and a number of groups have demonstrated antagonism. However, the response of T cells to an agonist ligand after encountering an antagonistic stimulus has not been previously characterized. Here, we show that T cells post-antagonism fail to proliferate but produce large quantities of IL-2 upon stimulation with their wild type ligand. This unique phenotype is not due to differences in IL-2 receptor expression or rates of apoptosis, and cannot be overcome by the addition of recombinant IL-2. The response of CD4 T cells to agonist stimulation after encountering an antagonist is a novel phenotype, and is distinct from previously described forms of anergy.

SHP1 Phosphatase-Dependent T Cell Inhibition by CEACAM1 Adhesion Molecule Isoforms

T cell activation through the T cell receptor (TCR) is subsequently modified by secondary signals that are either stimulatory or inhibitory. We show that CEACAM1 adhesion molecule isoforms containing a long cytoplasmic domain inhibited multiple T cell functions as a consequence of TCR ligation. Overexpression of CEACAM1 resulted in decreased proliferation, allogeneic reactivity, and cytokine production in vitro and delayed type hypersensitivity and inflammatory bowel disease in mouse models in vivo. Conditioned deletion of CEACAM1 in T cells caused increased TCR-CD3 complex signaling. This T cell regulation was dependent upon the presence of immunoreceptor tyrosine-based inhibition motifs (ITIM) within the cytoplasmic domain of CEACAM1 and the Src homology 2 domain-containing protein tyrosine-phosphatase 1 (SHP1) in the T cell. Thus, CEACAM1 overexpression or deletion in T cells resulted in T cell inhibition or activation, respectively, revealing a role for CEACAM1 as a class of inhibitory receptors potentially amenable to therapeutic manipulation.