Serum factors possessing some of the properties of the human rheumatoid factor(s) (RF) 1 have been produced in experimental animals. The RF and the experimentally induced factors react with various gamma globulins. The anti-gamma globulin specificities of experimentally induced serum factors can be attributed to one or more of the following mechanisms:(a) The production of antibodies against heterologous gamma globulin as in Adler's study (1) where sensitized sheep cell agglutinins developed in the serum of guinea pigs immunized with heterologous (rabbit) immune precipitates.(b) The production of iso-antibodies against rabbit gamma globulin of an allotype other than that of the host. (Studies of rabbit gamma globulin allotypes, references (9-12). This was probably operative in the studies of Milgrom and Dubiski (2, 3) who demonstrated sensitized sheep cell agglutinins in rabbits immunized with isologous antigen-antibody complexes (Escherickia coli and Proteus OX19 agglutinated by their respective rabbit antiserum). The hemagglutinating factor in each instance could be absorbed by some rabbit immune complexes but not by all.(c) Immunization against gamma globulin or gamma globulin products which were adsorbed or assimilated by bacteria, utilized for immunization, from either culture media or recent passage through animals. This was clearly

Systemic lupus erythematosus (SLE) and other connective tissue diseases (CTD) are characterized by a diverse antibody production which is generally not organ-or receptor-specific. Among these autoantibod--~

Radioimmunoassays for anti-F(ab')z antibodies, which feature the use of goat anti-human Fc antibody for correcting potentiation of IgM anti-F(ab')z antibody titers by endogenous IgM anti-Fc antibodies (rheumatoid factors), are described. Individuals with classic rheumatoid arthritis had significantly more IgM anti-F(ab')2 antibody (P < 0.001) and IgG anti-F(ab')2 antibody (P = 0.05) than did individuals with systemic lupus erythematosus or normal volunteers. There is some similarity in patterns of isotype distribution of anti-F(ab')z antibodies and rheumatoid factors.