A quantitative examination of the light scattering properties of immune complexes in polyethylene glycol.

The effect of polyethylene glycol on the light scattering properties of immune complexes prepared in vitro was examined. Immune complexes were prepared in the zone of antigen excess from purified rabbit anti-ovalbumin and ovalbumin at 2-32 times (X) the equivalence ratio. Immune complex concentration was determined by analytical ultracentrifugation. Immune complexes were then incubated for 1 h in solutions containing 0, 1, 2, 3 and 4% polyethylene glycol (PEG), and examined in a laser nephelometer. The effect of PEG on light scattering (%RLS) was different for each immune complex combining ratio, although for each immune complex combining ratio, there was a linear relationship between the light scattered and immune complex concentration. To evaluate the effect of serum proteins on the light scattered by the immune complexes, immune complexes made at 4X and 16X the equivalence ratio were placed in serum and the sera containing these immune complexes were examined in the nephelometer. The ratio of the %RLS of the immune complexes in serum to the sum of the %RLS of the same immune complexes in saline plus the %RLS of serum alone was determined. This ratio varied systematically with changes in combining ratio and PEG concentration, as well as the concentration of the immune complexes themselves. Depending on the combination of these 3 factors, serum could increase, decrease or have no effect on the quantity of light scattered by the immune complexes. Discrimination between serum alone and serum containing immune complexes was best in 3% PEG.