Experimental production of rheumatoid factor-like antibodies and antibodies against the cathepsin D site of IgG following the injection of autologous Fab2.

In a very high proportion of rabbits, repeated intra- or extra-articular injections of autolous Fab2 produced by homologous cathepsin D induce the formation of Rf-like antibodies reacting with both homologous and human IgG. Moreover, intra-articular injections of this kind cause a significant rise in the titre of thm of all the animals so far tested. Rf-like antibodies against human IgG appear earlier and have higher serum titres than those reacting with homologous IgG. The reason for this latter observation seems to be the blocking of the anti-rabbit IgG antibodies by the animal's own IgG. The anti-rabbit IgG antibodies can be absorbed only on aggregated rabbit IgG. The anti-human IgG antibodies cross-react to some extent with rabbit IgG. The results of inhibition studies suggest that the formation of anti-Fab2 homoreactants is directly stimulated by the injected Fab2, whereas the Rf-like antibodies owe their appearance to immune complexes formed in vivo by the injected Fab2 and the naturally occuring anti-Fab2 homoreactants. In respect of immunoglobulin class, the two kinds of Rf-like antibody are possibly of both IgM and IgG type.