Correlation of antiperinuclear factor with antibodies to streptococcal cell-wall peptidoglycan-polysaccharide polymers and rheumatoid factor

Antiperinuclear factor (APF) has been noted in most seropositive rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA) patients. The nature of the antigen is unknown; however, there are some suggestions that it might be a glycoprotein or proteoglycan. We studied the correlation of APF with antiproteoglycan antibodies and the reactivitity of IgM-rheumatoid factor (RF) with the perinuclear antigen. Ten serum samples were separated to IgG, IgM, and IgM-RF enriched fractions. In seven samples, APF was found in the IgG fraction. Only 4 had APF in their IgM rheumatoid factor (RF)-containing fraction. In two of these, APF activity was present solely in the IgM RF fraction and was inhibited by pre-incubation with IgG. Fifty-five JRA patients' sera were also tested for the presence of antibodies to Streptococcal cell wall peptidoglycan-polysaccharide polymers (PG-PSP). 76% of the APF-positive sera were anti-PG-PSP positive and 59% of the APF-negative sera were also anti-PG-PSP negative. Furthermore, 75% of the APF-positive sera lost their APF activity following adsorption to Streptococcal cell wall PG-PSP. Our results show that in JRA sera APF are polyclonal antibodies of both the IgG and IgM classes. Although the presence of APF correlates with RF positivity, and they sometimes may cross-react, many IgM RF-containing fractions do not show APF activity. However, the presence of APF does correlate with anti-PG-PSP positivity and the data suggest cross-reactivity between these two antibodies. This implies antigenic similarity between Streptococcal cell wall PG-PSP and the perinuclear antigen.