In Black Africans with rheumatoid arthritis, ACPA recognize citrullinated fibrinogen and the derived peptides α36-50Cit38,42 and β60-74Cit60,72,74, like in Caucasians

- Autoantibodies to citrullinated fibrin are good markers for RA in Black Africans.
- Their fine specificities (anti-α36-50 or β60-74) are similar to those of Caucasians.
- Like in Caucasians, the two specificities summarize 93% of the reactivity of ACPA.
- HLA-DRB1 SE alleles are associated with higher titres of autoantibodies.
- ACPA features are similar irrespective of genetic and environmental backgrounds.

Well documented in Caucasians and Asians, the diagnostic value of anti-CCP2 antibodies has been confirmed in Black African populations. However, autoantibodies to other citrullinated peptides/proteins and their fine specificities have not yet been studied. Here, we show that in Cameroonian patients, anti-citrullinated fibrinogen autoantibodies (AhFibA) are sensitive (73%) diagnostic markers for RA. We also determine that autoantibodies directed to α36-50Cit38,42 or β60-74Cit60,72,74 peptides which bear the immunodominant epitopes of citrullinated fibrin, are present in similar proportions in Black Africans and Caucasians with 25/56 (45%) and 41/56 (73%) positive RA-sera in Cameroonians, respectively. They also account for almost all the AhFibA reactivities since 38/41 (93%) AhFibA-positive sera contain anti-α36-50Cit38,42 and/or anti-β60-74Cit60,72,74 autoantibodies. Finally, HLA-DRB1 SE alleles were associated with higher titres of AhFibA and anti-β60-74Cit60,72,74 autoantibodies.In the genetic and environmental backgrounds of Black Africans, AhFibA are a hallmark of RA like in Caucasians, moreover they recognize the same fibrin epitopes.