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 reactivity 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.