PRTN3 and rheumatoid arthritis: However, less is known about the diagnostic and prognostic potential of measurement of ACPA and RF auto-antibodies of the IgA isotype in other ethnicities with RA, as well as their associations with prominent disease risk factors, specifically tobacco use (i.e. cigarettes and snuff) and positivity for the human leucocyte antigen - shared epitope (HLA-SE).