CD79A and rheumatoid arthritis: However, out of the five studies in the meta-analysis (23–27), only one small study (23), including 50 patients with RA, could demonstrate a significant association between antibodies to P. gingivalis and IgG ACPA and one study including 78 patients with RA (24) found an association between antibodies to P. gingivalis and IgM ACPA, but not IgG or IgA ACPA.