Lack of measurable complement fixing antibodies against viral antigens.

A serological and clinical study was performed to find the common features of 130 patients without antibodies against 11 or more different antigens in the complement fixation (CF) test. These patients (=1.6%) were discovered during hte screening of 8,021 adult patients. Rheumatoid factor(s) (RF) were found in the sera of 113 of the patients. In the remaining 17 patients no common serological or clinical markers were found. Myeloma M-components were found in three cases. The lack of measurable CF antibodies in RF positive cases was apparently due to the inhibitory effect of RF(s) in the CF test. This was indicated by a positive reaction in CF after centrifugal separation of IgM and IgG fractions and also by the detection of antibodies using immunodiffusion method. Possible immune complexes were sought using the platelet aggregation test, which was positive for the sera of 47 (=37%) of the patients. The clinical diagnosis of the 130 CF-nonreactors was rheumatoid arthritis (RA) (ARA criteria) in 23 cases and pulmonary diseases in 65 cases. In a comparison group of equal size there were only 3 RA patients and 15 with pulmonary disease. RA was thus found in 20% of the RF positive CF-nonreacting patients. In the comparison group of 52 RA patients 8 CF-nonreactors were found (=15%). This suggests that the effect of RF(s) from RA patients in CF reaction varies greatly.