[Methods and value of an immunofluorescence-optical determination of IgM, IgG and IgA rheumatoid factors]

Today the immuno-fluorescence technique is the simplest method to detect rheumatoid factors of all immuno-globulin classes. When applying sheep erythrocytes, standard sera may be used without exception. The airdried smear of the cells is to be incubated with rabbit anti-human-erythrocyte serum. The rheumatoid factors of the subsequently applied inactivated patients' sera localise above the amboceptor on the erythrocyte membrane. Only they bind FITC marked anti-human-gamma-globulin and cause a specific fluorescence. As a proof heteroagglutinines and crossreacting antibodies of the marked sera are first absorbed and corresponding controls are carried out. According to assessments of 101 sera approximately 20% of healthy people, approximately 50% of "definitely seronegative" patients with rheumatoid arthritis according to the agglutination method as well as 30% of other arthropathies had rheumatoid factors by these methods. A negative immunofluorescence optical test does not absolutely exclude the presence of rheumatoid factors in the serum. It is suggested that their occurrence are due to secondary reactions to the formation of immunogen antigen-antibody complexes.