Background/Purpose:   Emerging evidence suggests that the lungs may be an initiating site of autoimmunity leading to RA with organic inhalant exposures such as those from cigarette smoking acting as a trigger. To study the impact of organic inhalant exposures in RA pathogenesis, we previously developed a novel mouse model by exposing mice with collagen induced arthritis to repeated organic dust extract (ODE). Our objective in the present study was to evaluate autoantibody responses and tissue expression of extracellular matrix proteins (ECM) that have been implicated in RA pathogenesis and that may be involved in articular and lung responses in this model. 

Methods:   Male DBA/1J mice were injected with chicken collagen type II with Freund’s complete adjuvant (CIA) or saline on day 1 and 21.  ODE or saline was instilled by intranasal inhalation daily for 5 weeks. Groups are identified as: 1) Saline, 2) ODE, 3) CIA, and 4) ODE + CIA.  Anti-citrullinated protein antibody (ACPA) and IgG antibody to malondialdehyde-acetaldehyde (MAA) were measured in serum. Synovial and lung tissues were collected and stained for the presence of MAA, collagen II, fibronectin and vimentin. Confocal microscopy was used to assess tissue expression of ECM and MAA.  Coloc 2 plugin (ImageJ) was used to quantify correlations between the tissue expression of ECM and MAA.

Results:   Serum ACPA concentrations were significantly increased (p<0.05) in mice treated with ODE + CIA compared to all other treatment groups.  Anti-MAA levels were increased in the ODE exposed mice compared to Saline or CIA (p<0.0001) and decreased with the addition of ODE + CIA (p<0.02).  ECM and MAA expression mean pixel density in lung and joint tissues are shown in the Table 1. Paralleling enhanced arthritis and attenuated lung disease previously reported in ODE + CIA, differential colocalization of MAA with both collagen II and vimentin was observed in both synovium and lung (p<0.001) in ODE + CIA (Figure 1).  In contrast, fibronectin + MAA colocalization was similarly predominate in the lung in all groups.  

Conclusion:   Increased ACPA and decreased anti-MAA levels in the ODE + CIA treated group suggests a shift in the immune response with dual exposures. Likewise, ECM protein expression was markedly altered between synovium and lung in the combined ODE + CIA model. Our study importantly characterizes alterations in immune responses and ECM proteins that may explain the compartmentalized response of increase in inflammatory arthritis with the simultaneous attenuation of pulmonary disease previously observed in CIA mice exposed to ODE.