Association of Distinct Fine Specificities of Anti−Citrullinated Peptide Antibodies With Elevated Immune Responses to Prevotella intermedia in a Subgroup of Patients With Rheumatoid Arthritis and Periodontitis

Abstract

Objective In addition to the long-established link with smoking, periodontitis (PD) is also a risk factor for rheumatoid arthritis (RA). To elucidate the mechanism by which PD could induce antibodies to citrullinated peptides (ACPA), we examine the antibody response to a novel citrullinated peptide from cytokeratin type I 13 identified in gingival crevicular fluid (GCF), and compare the response to 4 other citrullinated peptides in patients with RA, well-characterized for PD and smoking. Methods The citrullinomes of GCF and periodontal tissue from people with PD were mapped by mass spectrometry. Antibodies to citrullinated peptides from cytokeratin type I 13 (cCK13), tenascin-C (cTNC5), vimentin (cVIM), enolase (CEP-1) and fibrinogen β (cFIBβ) were examined by ELISA in patients with RA (n=287) and osteoarthritis (OA) (n=330), and cross-reactivity assessed by inhibition assays. Results A novel citrullinated peptide cCK13-1 (444TSNASGR-cit-TSDV-cit-RP458) identified in GCF, exhibited elevated antibody responses in RA patients (24%). Anti-cCK13-1 antibodies correlated with anti-cTNC5 antibodies, and absorption experiments confirmed this was not due to cross-reactivity. Only anti-cCK13-1 and anti-cTNC5 were associated with antibodies to the periodontal pathogen Prevotella intermedia (p=0.05 and p =0.001 respectively), but not with antibodies to Porphyromonas gingivalis arginine gingipains. Antibodies to CEP-1, cFIBβ and cVIM correlated with each other, and with smoking and shared epitope risk factors in RA. Conclusion This study identifies two groups of ACPA fine specificities associated with different RA risk factors; one predominantly linked to smoking and shared epitope, the other linking anti- cTNC5 and cCK13-1 to infection with the periodontal pathogen P. intermedia.

Time to Include Fine Specificity Anti‐Citrullinated Protein Antibodies in the Routine Diagnosis and Management of Rheumatoid Arthritis?

“…Peptides from real autoantigens (fine specificities) tend to be of lower diagnostic sensitivity and are used primarily for research into disease pathogenesis, rather than clinical management. In a recent study , we found 2 groups of ACPA fine specificities associated with different RA risk factors. One, dominated by antibodies to citrullinated α‐enolase peptide 1 (CEP‐1), was linked to smoking and shared epitope as previously described .…”

“…We predict that this modest increase in sensitivity could be an underestimate caused by ascertainment bias because anti‐CCP2 positivity may have influenced the recruitment of patients to this cohort. In previous studies, using cohorts in which many of the patients were recruited before the CCP tests became available, anti–CEP‐1 and/or anti‐cTNC5 positivity was higher in the anti‐CCP2–negative RA patients, increasing overall diagnostic sensitivity by ~5% . Therefore, the inclusion of these 2 additional fine specificities at the point of diagnosis could increase the sensitivity even further, though clearly this needs to be confirmed in prospective studies.…”

“…We reanalyzed previous data from 287 patients with RA and 330 osteoarthritis controls, and we retested all of the sera for anti–CEP‐1 using a commercially available anti–CEP‐1 enzyme‐linked immunosorbent assay (Euroimmun), optimized for clinical use. The diagnostic sensitivity with anti–CEP‐1 was increased from 39% to 48%, with a specificity of 98%. We then examined whether the addition of anti–CEP‐1 and anti‐cTNC5 to CCP2 increased the overall diagnostic sensitivity.…”

Insights into the study and origin of the citrullinome in rheumatoid arthritis

“…One such mechanism is citrullination. Proteomic analysis of gingival crevicular fluid (GCF) and periodontal tissue from patients with periodontitis with and without RA has shown abundant citrullination that overlaps with the RA citrullinome, supporting the notion that periodontitis is a potential source of citrullinated autoantigens. Mechanisms that dysregulate citrullination in periodontitis have been mainly attributed to periodontal pathogens, in particular Porphyromonas gingivalis ( P gingivalis ) and Aggregatibacter actinomycetemcomitans ( Aa ) .…”

Biological links in periodontitis and rheumatoid arthritis: Discovery via text‐mining PubMed abstracts

“…The keystone periodontal pathogen P. gingivalis is the sole human pathogen known to produce a peptidylarginine deiminase (PPAD) enzyme which can citrullinate host proteins, and is believed to be an initiator of ACPA production . Emerging reports suggest other known periodontal pathogens P. intermedia can also induce specific ACPA . While a large set of experimental studies exist, the scale of putative molecular mechanisms underlying PD and RA comorbidity may be revealed by primary gene expression studies.…”