Antibodies against macaque monoclonal immunoglobulin G in rheumatoid arthritis

The presence of rheumatoid factors (RF) in the serum of rheumatoid arthritis (RA) patients is commonly evidenced by agglutination tests: the Waaler-Rose assay, based on the use of human red blood cells (RBCs) coated with rabbit anti-RBC antibodies, and the latex test, which uses latex particles coated with denatured human immunoglobulin G (IgG). The aim of the present study was to characterize the RF able to agglutinate human RBCs coated with macaque antihuman RBC IgG antibodies secreted from macaque-mouse heterohybridomas (two from rhesus monkey and one from crab-eating macaque). Human RBCs coated with macaque monoclonal antibodies (MacMoAbs) were used for agglutination tests and these were carried out in parallel with standard tests (Waaler-Rose and latex agglutination tests) on sera from 82 RA patients, 86 patients with other forms of inflammatory chronic arthritis and 47 healthy human subjects. MacMoAb-coated RBCs identified RF in the sera of 66% patients with RA. By contrast, the frequency of positive sera in other inflammatory diseases was 5% and all 47 healthy controls were negative. Antimacaque IgG antibodies were found to be more specific for RF than standard tests, in the sera of patients with RA.