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OBJECTIVE: Autoimmune regulator (Aire) promotes the ectopic expression of tissue-restricted antigens in medullary thymic epithelial cells (mTECs), leading to negative selection of autoreactive T cells. This study was undertaken to determine whether loss of central tolerance renders Aire-deficient (Aire(-/-)) mice more susceptible to the induction of autoimmune arthritis. METHODS: Medullary TECs were isolated from Aire(-/-) and wild-type C57BL/6 mice for gene expression analysis. Collagen-induced arthritis (CIA) was elicited by injection of chick type II collagen (CII) in adjuvant. Cellular and humoral immune responses to CII were evaluated. Chimeric mice were created by reconstituting lymphocyte-deficient mice with either Aire(-/-) or wild-type CD4 T cells and wild-type B cells. RESULTS: Wild-type, but not Aire(-/-), mTECs expressed the CII gene Col2a1. Aire(-/-) mice developed more rapid and severe CIA, showing elevated serum anti-CII IgG levels, with earlier switching to arthritogenic IgG subclasses. No evidence was found of enhanced T cell responsiveness to CII in Aire(-/-) mice; however, Aire(-/-) CD4 T cells were more efficient at stimulating wild-type B cells to produce anti-CII IgG following immunization of chimeric mice with CII. CONCLUSION: Our findings indicate that Aire-dependent expression of CII occurs in mTECs, implying that there is central tolerance to self antigens found in articular cartilage. Reduced central tolerance to CII in Aire(-/-) mice manifests as increased CD4 T cell help to B cells for cross-reactive autoantibody production and enhanced CIA. Aire and central tolerance help prevent cross-reactive autoimmune responses to CII initiated by environmental stimuli and limit spontaneous autoimmunity. [ABSTRACT FROM AUTHOR]

Amino acid variants of an antigenic peptide or altered peptide ligands have previously been investigated with CD4+ and CD8+ T cells. However, for CD8+ T cells, only clones (which are continually restimulated in vitro) have been assessed. Using TCR transgenic mice specific for a class I Kb-restricted OVA peptide (OVAp; OT-I mice) as a source of naïve CD8+ T cells, single amino acid variants of the OVAp were analysed in vitro for their ability to antagonize the proliferative and cytotoxic function of naïve OT-I cells. Peptides with substitutions at TCR contact residues were found to be the most potent antagonists of OT-I cell function. Those peptides that inhibited activation of cells to proliferate also inhibited activation of cells to become killers. Inhibition was inversely correlated with interferon (IFN)-γ production. It was found that levels of antagonist peptide required for inhibition were higher than that described for T cell clones, presumably due to affinity differences. [ABSTRACT FROM AUTHOR]

During investigations into the behaviour and fate of ovalbumin (OA)-specific CD8+ T cells in a TCR transgenic system, cytotoxic T lymphocyte (CTL) activity (as measured by classical in vitro stimulation followed by 51CR-release assay) was found to be reduced after OVA peptide administration. This paradoxically occurred even during the peak of activation and expansion of these T cells. The reduced responsiveness occurred for both classical CTL assays and in vitro proliferation assays, and would apparently be consistent with induction of anergic or suppressor T cells. Instead, we provide evidence that in vivo peptide treatment generated activated killers which consequently killed the stimulator cells during in vitro culture, thus resulting in the unresponsive phenotype. In co-culture experiments, the proliferation and classical CTL activity were severely reduced when naive OVA-specific CD8+ T cells (OT-1) cells were co-cultured with cells from OVA peptide-treated mice. Moreover, cells obtained after peptide injection did not require in vitro stimulation to be able to kill target cells. Therefore, activation of killers in vivo should be considered as one pathway whereby unresponsiveness is found in assays requiring in vitro stimulation. [ABSTRACT FROM PUBLISHER]