In a genetically predisposed population of NAN patients with RA and their relatives, anti-P. gingivalis antibodies were associated with ACPA. These findings suggest that immune responses to P. gingivalis may be involved in breaking immune tolerance to citrullinated antigens.

Rheumatoid arthritis (RA) is one of the most common autoimmune diseases, and affects 0.5-1% of the population. Although it poses a considerable health problem, relatively little remains known about the disease pathogenesis and etiology. In the past decade, anti-citrullinated protein antibodies (ACPA) have emerged as suspects in the development and/or progression of RA. Citrullinated proteins--containing the amino acid citrulline, generated post-translationally from arginine--are found in the joints of patients with RA, but are not specific for the disease. This situation contrasts with the presence of ACPA, which are mostly found in individuals with RA. Intriguingly, ACPA can also be found in individuals before symptom onset. In these instances the ACPA response seems to be in its infancy, recognizing only a few citrullinated antigens and not using the full isotype repertoire. These characteristics of the ACPA response mature before clinical disease precipitates. Evidence is emerging that ACPA status can further characterize the heterogeneous RA phenotype, not only with respect to outcome, but perhaps also with respect to intervention. This Review summarizes the evolution of the ACPA response and its putative role in disease pathogenesis, as well as its relationship with clinical phenotype and diagnostic potential.

The vast majority of ACPA-IgG harbour N-glycans in their variable domains. As N-linked glycosylation requires glycosylation consensus sites in the protein sequence and as these are lacking in the 'germline-counterparts' of identified variable domains, our data indicate that the N-glycosylation sites in ACPA variable domains have been introduced by somatic hypermutation. This finding also suggests that ACPA-hyperglycosylation confers a selective advantage to ACPA-producing B cells. This unique and completely novel feature of the citrulline-specific immune response in RA elucidates our understanding of the underlying B cell response.

Objective. Anti-citrullinated protein antibodies (ACPAs) display high association with rheumatoid arthritis (RA) and are implicated in its pathogenesis. The presence of ACPAs is known to precede the onset of RA. In order to identify the features that could confer its pathogenicity, we extensively characterized this antibody response in a unique North American native population of patients with RA and their unaffected relatives.Methods. The levels of IgA, IgM, and IgG ACPAs, as well as IgM and IgA rheumatoid factor (RF), were measured in serum samples obtained from 81 patients with RA and 195 of their unaffected relatives. The isotype distribution, the fine specificity of the ACPA response, and its association with RF were compared in health and disease.Results. ACPA positivity was observed in 19% of the healthy relatives and ϳ91% of the patients with RA. ACPA isotype usage was strikingly lower in unaffected relatives than in patients with RA (1-2 versus 5-6 isotypes). Fine specificity studies showed that reactivity to citrullinated fibrinogen and vimentin was present in sera from patients with RA, while it was virtually absent in their unaffected relatives. Finally, the ACPA and RF responses were associated in patients with RA but were discordant in their healthy relatives. Extended analyses revealed that the presence of ACPAs was associated with RA irrespective of RF status, while the association of RF with disease relied on its interaction with ACPAs.Conclusion. The fine specificity and isotype usage of the ACPA response are qualitatively different in health and disease. Epitope spreading and expansion of the isotype repertoire might be necessary for development of RA, and this could be facilitated by the presence of RF antibodies.Autoantibodies are characteristic of a large number of autoimmune diseases. Determining the pathogenicity of autoantibodies by showing their capacity to transfer disease, however, is complicated by ethical and practical difficulties. Therefore, only a small minority of autoantibodies, such as antiplatelet antibodies in idiopathic thrombocytopenia purpura or the antidesmoglein antibodies in pemphigus vulgaris, were convincingly shown to mediate a pathogenetic effect through placental transfer (1) or transfer into experimental animals (2), respectively.

Langerhans cell histiocytosis (LCH) is characterized by a clonal proliferation and retention of cells with a Langerhans cell (LC)-like phenotype at various sites within the body. The present study set out to elucidate whether aberrant expression of chemokine receptors or dysregulation of chemokine production in LCH lesions could explain abnormal retention of these cells. Immunohistochemical analysis on 13 LCH biopsies of bone, skin, and lymph node all expressed the immature dendritic cell (DC) marker CCR6 on the lesional LCs and absence of the mature DC marker CCR7. Furthermore, regardless of the tissue site, LCH lesions markedly overexpressed CCL20/MIP-3α, the ligand for CCR6. The lesional LCs appeared to be the source of this CCL20/MIP-3α production as well as other inflammatory chemokines such as CCL5/RANTES and CXCL11/I-TAC. These may explain the recruitment of eosinophils and CD4+CD45RO+ T cells commonly found in LCH lesions. The findings of this study emphasize that, despite abundant TNF-α, lesional LCs remain in an immature state and are induced to produce chemokines, which via autocrine and paracrine mechanisms cause not only the retention of the lesional LCs but also the recruitment and retention of other lesional cells. We postulate that the lesional LCs themselves control the persistence and progression of LCH.