Objective. Recent data suggest that a geneenvironment interaction between smoking and the HLA shared epitope alleles plays a role in shaping the autoimmune reaction to specific citrullinated antigens. This study was undertaken to determine the effects of HLA shared epitope alleles and tobacco exposure on the immune response against various citrullinated antigens. These associations were analyzed in the anticitrullinated protein antibody (ACPA)-positive stratum to control for the possibility that the associations found are explained by the known interaction between HLA shared epitope alleles and tobacco exposure on ACPA status.
Methods. In 661 patients with rheumatoid arthri-tis, reactivity against several citrullinated antigens from vimentin, fibrinogen, enolase, and myelin basic protein was determined by enzyme-linked immunosorbent assay. The effects of the HLA shared epitope alleles and tobacco exposure were assessed by logistic regression analysis. Biologic interaction was analyzed by investigating whether the effects of the risk factors combined exhibited departure from additivity.
Results. A significant interaction between tobacco exposure and HLA shared epitope alleles was found for the presence of ACPA as reported previously. When these interaction effects were studied for several ACPA "fine specificities," significant interactions were noted for several citrullinated peptides. However, these interactions were not present after stratification for ACPA status, indicating that the interaction between tobacco exposure and HLA shared epitope alleles influences autoimmunity not to specific citrullinated antigens, but rather to ACPA development.
Conclusion.
Our data indicate that the geneenvironment interaction between HLA shared epitope alleles and smoking does not appear to shape the reactivity of the ACPA response. These data suggest that smoking promotes nonspecific citrullination rather than citrullination of specific antigens.
Rheumatoid arthritis (RA) is a systemic autoimmune disease involving inflammation of the joints. The detection of anti-citrullinated protein antibodies (ACPAs), often measured by an anti-citrullinated antibody assay (anti-cyclic citrullinated peptide 2 [anti-CCP-2]), is an accepted diagnostic tool for RA (1). Anti-CCP antibodies are highly specific for RA, can be detected years before the first clinical manifestation of