Microchimeric cells promote production of rheumatoid arthritis-specific autoantibodies

Women are more likely to develop autoimmune diseases than men. Contribution from microchimerism (Mc) has been proposed, as women naturally acquire Mc from more sources than men because of pregnancy. Women with Rheumatoid Arthritis (RA) who lack RA-associated HLA alleles have been found to harbor Mc with RA-associated HLA alleles in higher amounts than healthy women in prior work. However, an immunological impact of Mc remains to be elucidated.

To test the hypothesis that Mc with RA-risk associated HLA alleles can result in the production of RA-associated autoantibodies, when host genetic risk is absent.

DBA/2 mice are unable to produce RA-specific anti-citrullinated autoantibodies (ACPAs) after immunization with the enzyme peptidyl arginine deiminase (PAD) in a previously developed model. DBA/2 females were mated with C57BL/6 males humanized to express HLA-DR4, which is associated with RA-risk and production of ACPAs, to evaluate DR4+ fetal Mc contribution. Next, DBA/2 females born of heterozygous DR4^+/- mothers were evaluated for DR4+ Mc of maternal or littermate origin. Finally, DBA/2 females from DR4^+/- mothers were crossed with DR4⁺ males, to evaluate the contribution of any Mc source to ACPA production.

After PAD immunization, between 20 % and 43 % of DBA/2 females (otherwise unable to produce ACPAs) had detectable ACPAs (CCP2 kit) after exposure to sources of Mc with RA-associated HLA alleles, compared to 0 % of unmated/unexposed DBA/2 females. Further the microchimeric origin of the autoantibodies was confirmed by detecting a C57BL/6-specific immunoglobulin isotype in the DBA/2 response.

Our study demonstrates that Mc cells can produce "autoantibodies" and points to a role of Mc in the biology of autoimmune diseases, including RA.