Rheumatoid arthritis specific autoimmunity in the lung before and at the onset of disease.

OBJECTIVE: The lung is implicated as a site for breaching tolerance prior to onset of seropositive RA. To substantiate this, we have investigated lung-resident B cells in bronchoalveolar lavage (BAL) samples from early untreated RA patients (n=9) and anti-citrullinated protein antibody (ACPA)-positive individuals at risk of developing RA (n=3).

METHODS: Single B cells (n=7680) were phenotyped and isolated from BAL of individuals during the risk-RA phase and at RA diagnosis. The Immunoglobulin variable region transcripts were sequenced and selected for expression as monoclonal antibodies (n=141). Monoclonal ACPAs were tested for reactivity patterns and binding to neutrophils.

RESULTS: By our single cell approach, we found significantly increased proportions of B lymphocytes in autoantibody-positive as compared to negative individuals. Memory and double negative (DN) B cells were prominent in all subgroups. Upon antibody re-expression, seven highly mutated citrulline autoreactive clones originating from different memory B cell subsets where identified, both in at-risk and early RA patients. Lung IgG variable gene transcripts from ACPA-positive individuals carry frequent mutation-induced N-linked Fab glycosylation sites (p<0.001), often in the framework-3 of the variable region. Two of the lungs ACPAs bound to activated neutrophils, one from an at-risk individual and one from early RA.

CONCLUSION: We conclude that T cell driven B cell differentiation, resulting in local class switching and somatic hypermutation are evident in lungs before, as well as in, early stages of ACPA-positive RA. Our findings add to the notion of lung mucosa being a site for initiation of the citrulline autoimmunity preceding seropositive RA. This article is protected by copyright. All rights reserved.