Rabbits immunized with mixtures of staphylococcal protein A and autologous IgG produce anti-human IgG antibodies

Triggering of renal tissue damage in the rabbit by IgG Fc-receptor-positive group A streptococci

Our previous studies have shown that streptococcal IgG Fc receptors (FcR) act to elicit circulating anti-IgG as well as renal glomerular deposition of IgG in rabbits immunized with group A streptococci (GAS). In order to study if other FcR-positive bacteria might have similar effects, rabbits were immunized with either group G streptococci (GGS; strain G148) or Staphylococcus aureus (strain Cowan I) for two periods of 8 and 6 weeks, respectively. At the end of immunization, circulating anti-IgG was found in 6 of 20 (30%) and 4 of 19 (21%) animals receiving G148 and Cowan I, respectively, compared to all 28 receiving FcR-positive GAS strains of types M1, M4, M15 or M22 (p < 0.05 for both comparisons); furthermore, anti-IgG appeared earlier and at higher levels in the GAS groups. Weak glomerular IgG deposits occurred in 5 out of 10 (50%) and 2 out of 8 (25%) animals immunized with G148 and Cowan I, respectively. In contrast, all 11 rabbits examined, given GAS of types M1 or M15, displayed heavy deposits. None of four control animals immunized with either of two FcR-negative strains, GAS type T27 or group B streptococci (GBS) type Ia, exhibited any renal IgG deposits or circulating anti-IgG. Renal tissue materials from rabbits immunized with any of the four FcR-positive GAS strains showed strong inflammatory and degenerative glomerular changes, compatible with the picture seen in acute poststreptococcal glomerulonephritis (APSGN). Only transient renal changes were found in those rabbits immunized with G148 or Cowan I, or the controls injected with the FcR-negative strains, GAS type T27 or GBS. Thus, only the FcR-positive GAS strains showed capacity to induce high levels of anti-IgG, pronounced tissue deposition of IgG as well as irreversible glomerular changes. Our experimental data suggest that streptococcal IgG FcR activity might play an important role in triggering APSGN.

Development of rheumatoid factor research through 50 years

The discovery of Waaler in 1937 initiated fruitful research on RFs. It was not until the early 1960s that investigators in the field agreed that RFs are antibodies to Fc fragment of IgG. Separate factors combining with human and rabbit IgG and a factor combining with both these IgGs were at first demonstrated by mixed agglutination and then by separation through IgG-conjugated columns. Only RF combining with native autologous IgG should be considered an autoantibody. Other RFs are allo- or heteroantibodies. Cross-reacting RFs that combine with IgG of various species or with IgG and antigens of cell nuclei are of considerable interest. This cross-reactivity may be due to a combining site interacting with shared epitopes or otherwise to multispecificity of the RF molecule in that it has separate or partially overlapping combining sites acting on different epitopes. Experimental studies conducted since the mid-1950s showed that formation of RFs may be elicited by altered autologous IgG. Under natural conditions such alteration was shown to result from interaction of IgG antibody with its corresponding antigen and RF in many infectious diseases and possibly also in rheumatoid arthritis appeared to result from stimulation by immune complexes. More recently alterations of IgG by its reaction with microbial Fc receptors as well as non-specific polyclonal stimulation of B cells were shown to play a role in RF formation. RFs have been implemented in the pathogenicity of rheumatoid arthritis. Recent studies on dispersion of immune complexes in tissue sections by aggregated IgG showed that self-polymerization of IgG RFs results in formation of glomerular deposits in various nephropathies.