Multispecificity of monoclonal rheumatoid factor.

The study involved a monoclonal rheumatoid factor referred to as RF-AN, obtained by Steinitz and his associates from IgG-reactive human lymphocytes 'immortalized' by infection with Epstein-Barr virus. RF-AN combined with red blood cells (RBC) sensitized by either human or rabbit IgG antibodies. The monoclonal character of RF-AN strongly suggested that the same molecule of this factor combined with IgG of both species. Additional evidence for this contention was obtained from absorption and mixed agglutination experiments. RBC sensitized by either human or rabbit antibodies would remove serological activity of RF-AN for both human and rabbit IgG. RF-AN produced exclusively mixed agglutinates when reacted with a mixture of human RBC sensitized by human antibodies and chicken RBC sensitized by rabbit antibodies. Furthermore, it was shown that inhibition with aggregated human Fraction II gave strictly 'specific' results in that it abolished the reaction of RF-AN with RBC sensitized by human antibodies, but not by rabbit antibodies. This result was interpreted as indicating that RF-AN has a multispecific character, i.e., has separate combining sites for human and rabbit IgG. Interestingly, specific inhibition could not be achieved with aggregated rabbit Fraction II and this preparation affected reactivity of RF-AN with RBC sensitized by human antibodies as well as by rabbit antibodies.

Are cross-reacting natural antibodies multispecific?

Human natural antibodies to antigens of Escherichia coli and Serratia marcescens were studied for cross-reactivity. The organisms were grown on synthetic media and extracted at 100 degrees C. The extracts were precipitated three times at 71% ethanol concentration and redissolved at the desired concentration. These preparations were referred to as Escherichia antigen (Ea) and Serratia antigen (Sa). They readily coated red blood cells (RBC), which then could be used for passive agglutination tests. Human serum selected for this study had strong agglutinins combining with both antigens (cross-reacting antibody) and rather weak agglutinins combining with Ea only or Sa only, a property that became obvious from absorption experiments. Absorption of the serum with RBC coated by Ea removed all activity for Ea and most of the activity for Sa, and the opposite effect was noted after absorption of the serum by RBC coated by Sa. The activity against both antigens could be recovered by elution of antibodies at 56 degrees C from RBC coated by either Ea or Sa. Significantly, inhibition of the serum or the eluate with soluble antigens gave strictly specific results in that Ea abolished only the reaction with RBC coated by Ea and did not influence the reaction of RBC coated by Sa, and the opposite result was obtained upon inhibition of the serum with Sa. These results strongly indicated to us that the cross-reacting antibodies under study were multispecific, i.e., had different antigen-reactive sites (haptophore groups) for Ea and Sa. Further evidence supporting this contention was obtained from a study in which the cross-reacting antibody was 'labelled' by a bacterial antigen. To this end, the tested serum was neutralized with Sa and then reacted with RBC coated by Ea. From these RBC, antibodies were eluted from which Sa was recovered. A 'mirror image' experiment was also conducted in which Ea was recovered from antibodies that were blocked by Ea and reacted with RBC coated by Sa.

Lack of circulating immune complexes in inflammatory bowel disease.

Multi-organ involvement and especially extraintestinal manifestations have suggested an immune complex-mediated pathogenesis of ulcerative colitis and Crohn's disease. Using various techniques controversial data have been reported on the incidence and levels of circulating immune complexes and their correlation to clinical presentation. Sera of 131 patients with inflammatory bowel disease (78 Crohn's disease, 53 ulcerative colitis) representing a wide spectrum of disease activity, treatment and presence or absence of extraintestinal manifestations were tested for circulating immune complexes using Raji cell indirect immunofluorescence assay, Raji cell radioimmunoassay, C1q solid phase assay and polyethylene glycol precipitation coupled with measurements of optical density and subsequent immunoelectrophoresis or radial immunodiffusion. Circulating immune complexes in low concentrations were observed in a small number of patients with inflammatory bowel disease, the frequency and concentrations being slightly higher in patients with Crohn's disease than in those with ulcerative colitis. No association of concentrations of circulating immune complexes with disease activity or presence of extraintestinal manifestations could be demonstrated. These data do not support the claim for a major role of circulating immune complexes in the pathogenesis of inflammatory bowel disease.

Comparison of some procedures detecting circulating immune complexes.

Tests for circulating immune complexes were performed by means of 1) plain polyethylene glycol (PEG) precipitation (PEGprec), 2) immunoelectrophoresis of PEG precipitates (IEpp), 3) anti-antibody (AA) inhibition test with sera (AA-Is), and 4) AA inhibition test with PEG precipitates (AA-Ipp). The tests were performed with 156 pathological sera from patients with myasthenia gravis, syphilis, adenocarcinomas of the gastrointestinal tract, rheumatoid arthritis and systemic lupus erythematosus, and 51 normal sera from blood donors. PEGprec was positive with 76 sera, IEpp with 84 sera, AA-Is with 64 sera, and AA-Ipp with 74 sera. Comparison of results in all four tests showed high degree of correlation; all p values were below 0.005. The lower sensitivity of AA inhibition tests was due to the fact that these tests detect only complexes formed by IgG but not by IgM, whereas the remaining two tests detect complexes formed by antibodies of both these immunoglobulin classes. When sera of patients with rheumatoid arthritis and SLE were removed from the material studied, the four tests showed about equal sensitivity. PEGprec gave positive results with two normal sera and the remaining tests were negative with all these sera. It appears that the simultaneous application of PEGprec, IEpp, AA-Is and AA-Ipp will give sensitive and reliable procedure for detecting circulating immune complexes.

Circulating immune complexes in systemic scleroderma.

Circulating immune complexes were detected by the immunoelectrophoretic method in 18 of 29 (62 per cent) of patients with systemic scleroderma. The presence of immune complexes did not correlate with that of antinuclear antibodies to dsDNA, DNP, RNP, and Sm. The mean levels of immunoglobulins G, A, and M as well as of C3 were significantly higher in patients with systemic scleroderma than in blood donors.