ABSTRACT
OBJECTIVE: Antibodies directed against citrullinated proteins (ACPAs) are highly specific for rheumatoid arthritis (RA). The production of ACPAs is most likely dependent on the presence of T cells, since ACPAs undergo isotype switching and are associated with the shared epitope (SE)-containing HLA-DRB1 alleles. Vimentin is a likely candidate protein for T cell recognition, since >90% of patients positive for ACPAs that are reactive with (peptides derived from) citrullinated vimentin carry SE-containing HLA-DRB1 alleles. The aim of this study was to identify citrullinated vimentin peptides that are presented to HLA-DRB1*0401-restricted T cells. METHODS: HLA-DR4-transgenic mice were immunized with all possible citrulline-containing peptides derived from vimentin, and T cell reactivity was analyzed. Peptides recognized in a citrulline-specific manner by T cells were selected and analyzed for their ability to be processed from the entire vimentin protein. A first inventory of the selected epitopes recognized by T cells was performed using peripheral blood mononuclear cells (PBMCs) from ACPA+, HLA-DR4+ patients with RA. RESULTS: A citrulline-specific response was observed for 2 of the peptides analyzed in DR4-transgenic mice. These peptides were found to be naturally processed from the vimentin protein, since citrullinated vimentin was recognized by peptide-specific T cells. T cell reactivity against these peptides was also observed in cultures of PBMCs from RA patients. CONCLUSION: This study identifies, for the first time, 2 naturally processed peptides from vimentin that are recognized by HLA-DRB1*0401-restricted T cells in a citrulline-specific manner. These peptides can be recognized by T cells in ACPA+, HLA-DR4+ patients with RA, as shown in a first inventory.
Subject(s)
Arthritis, Rheumatoid/immunology , Autoantibodies/blood , HLA-DR4 Antigen/immunology , Peptides, Cyclic/immunology , T-Lymphocytes/immunology , Vimentin/immunology , Adult , Aged , Animals , Arthritis, Rheumatoid/blood , Epitope Mapping , Epitopes , Female , HLA-DR4 Antigen/genetics , Humans , Leukocytes, Mononuclear/immunology , Male , Mice , Mice, Transgenic , Middle Aged , Peptides, Cyclic/chemistry , Vimentin/chemistry , Vimentin/geneticsABSTRACT
Expression of the transcription factor Foxp3 (forkhead box P3) has been implicated as a key element for CD25(+) T regulatory cell function in mice. However, literature over similar involvement of FOXP3 expression in human T regulatory cells is limited. We found that, unlike murine cells, FOXP3 mRNA expression could be induced in human CD25(-) and CD8(+) peripheral blood mononuclear cells, which were both negative for FOXP3 mRNA expression after isolation. Expression of FOXP3 mRNA began as soon as 24-40 hours after stimulation, demonstrating a correlation between activation and FOXP3 mRNA expression in human cells. In order to determine whether FOXP3 expression is confined to CD4(+)CD25(+) T cells with a regulatory phenotype, we analyzed several well-defined T-cell clones and lines with various specificities. Surprisingly, expression of FOXP3 mRNA was detected in all clones and limited to the CD25(hi) populations. Nonetheless, the CD25(hi) fraction did not display regulatory properties because both the CD25(hi) and CD25(low) populations exhibited a similar proliferative- and interferon-gamma-secreting potential after antigenic stimulation. These results indicate that FOXP3 expression in humans, unlike mice, may not be specific for cells with a regulatory phenotype and may be only a consequence of activation status.
