Associations to smoking and shared epitope differ between IgA and IgG class antibodies to cyclic citrullinated peptides in early rheumatoid arthritis

• Background Smoking and HLA-DRB1/shared epitope (SE) are well-known interacting risk factors for developing rheumatoid arthritis (RA) with IgG anticitrullinated protein/peptide antibodies (ACPA). It remains unknown to what extent SE-genes and smoking associate with mucosal immune responses.Objectives This study was done to explore relations between cigarette smoking habits and SE versus circulating IgA and IgG anti-cyclic citrullinated peptide antibodies (anti-CCP) among early RA patients.Methods Patients from two early-RA cohorts were analysed, EIRA-1 (n=1663) and TIRA-2 (n=199). The patients were grouped into four subsets based on anti-CCP: IgG-/IgA-, IgG-/IgA+, IgG+/IgA- and IgG+/IgA+. Interaction between smoking and SE was calculated by the attributable proportion due to deviation from additivity. Analyzed controls (n=1100) were randomly selected from the EIRA-1 study base.Results Anti-CCP occurrence was similar in the two cohorts. Only in EIRA was IgA anti-CCP detected alone in a minority of cases (3%). Smoking was significantly overrepresented among IgA anti-CCP+ patients with or without IgG-class anti-CCP, but not with IgG anti-CCP alone. Presence of SE genes was overrepresented among IgG anti-CCP+ patients with or without IgA-class anti-CCP, but not with IgA anti-CCP alone. Smoking and SE interacted regarding the risk of IgG+/IgA+ RA (AP=0.5, 95 % CI=0.4-0.6), whereas no significant interaction was observed regarding IgG-/IgA+ or IgG+/IgA- RA.Conclusions Association between cigarette smoking and anti-CCP is limited to cases with IgA-class antibodies in addition to IgG anti-CCP. This suggests a causal relation between chronic mucosal irritation/inflammation, induction of a systemic IgA anti-CCP response and subsequent development of RA.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Reumatologi och inflammation (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Rheumatology and Autoimmunity (hsv//eng)

Nyckelord

Rheumatoid arthritis

immunoglobulin A

ACPA

smoking

shared epitope

MEDICINE

MEDICIN

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