Quantitative studies of immunofluorescent staining. IV. Indirect immunofluorescence blocking tests with anti-perinuclear factors of human and goat origin.

The antiperinuclear factor (APF) is found in a high percentage of sera from patients with rheumatoid arthritis. It can be demonstrated by direct immunofluorescence using the keratohyaline granules of human buccal mucosa as antigenic substrate. Mixing of some normal goat sera with an APF positive serum from a patient with rheumatoid arthritis resulted in an inhibition of the APF titre of the patient's serum. However, there was no clear cut correlation between the APF-positivity of normal goat sera and their inhibitory effect on the APF-reactivity of a human rheumatoid arthritis patient's serum. In reciprocal screening tests the human rheumatoid arthritis serum blocked only one of the APF-reactive goat sera. The reciprocal blocking activity of this goat serum and the patient's serum could be more exactly evaluated by the use of chessboard titrations in an indirect immunofluorescence blocking test. This test consisted of mixing equal volumes of serial dilutions of a goat serum and the patient's serum and subsequent examination of the mixtures for APF using an anti-human IgG conjugate and an anti-goat immunoglobulin conjugate, respectively. The results point to an antibody nature for the APF in preimmune, normal goat sera and to the value of chessboard titrations of this type in demonstrating the identity, non-identity, partial identity (or very close proximity of antigenic determinants) of the antibodies in different antisera which cannot be distinguished by their immunofluorescent staining patterns.