THE FORMATION OF INSOLUBLE IMMUNE-COMPLEXES BETWEEN OVALBUMIN AND ANTI-OVALBUMIN IGG OCCURS IN AT LEAST 2 DISTINCT PHASES DEPENDENT ON REACTANT CONCENTRATION AND IONIC-STRENGTH

The mechanism regulating the formation of insoluble immune complexes ( IIC) in serum in certain disease states is not well understood. Ovalbu min and rabbit anti-ovalbumin IgG was used to study the formation of I IC in vitro in a stirred reaction vessel; and the radii of IIC that fo rmed was determined by light scattering techniques. Using an initial I gG concentration of 1 mg/ml at equivalence antigen:antibody ratio IIC formation was detected within 5 s, and the complexes increased in radi i to approx. 100 nm after 20-30 s (phase 1). This was followed by a ph ase (phase 2) in which the complexes rapidly increased in radii to the point where Mie scattering was reached (similar to 200 nm). The time of onset of the second phase decreased with increasing initial IgG con centrations at a fixed antigen:antibody ratio; and was at a minimum at equivalence antigen:antibody ratio, but increased at both antigen and antibody excess ratios. Immune complexes formed using F(ab')(2) fragm ent showed a similar pattern to those formed using IgG. A similar patt ern was seen in the presence of the complement component Clq which pot entiated IIC formation in phase 2, and human serum (1:10 dilution) whi ch attenuated IIC formation in both phases. For complex formation usin g IgG and ovalbumin the presence of NaCl at concentrations up to 0.6 M led to a progressive increase in the time of onset of phase 2; potenc ies of inhibition by other sodium halides followed the lyotropic serie s NaF < NaCl < NaI. The results suggest that formation of IIC occurs i n at least two distinct phases, and that the second phase leading to t he generation of very large insoluble complexes is associated with a r apid polymerisation of the complexes by a mechanism that is not depend ent on Fc:Fc interactions.