Detection of immune complexes in serum of dogs with neoplastic disease by solid-phase C1q binding, using an enzyme-linked immunosorbent assay.

A solid-phase C1q-binding assay for detection of serum immune complexes (IC) was modified for an enzyme-linked immunosorbent antibody method. The IC values were measured in sera from 25 clinically normal dogs and 74 dogs with histologically confirmed neoplastic disease. Serum IC values were expressed in micrograms of heat-aggregated canine immunoglobulin per milliliter that would produce equivalent binding under the same assay conditions. The IC concentrations in sera from normal dogs and dogs with neoplastic disease (mean +/- SD) were 98 +/- 45 and 701 +/- 1,409 micrograms of aggregated canine immunoglobulin G equivalents/ml, respectively. Concentrations in the clinically normal group appeared to be distributed normally and clustered around the middle range of IC values. Dogs with neoplasms had IC values with an irregular distribution, and in general, more dogs had high and low concentrations of IC compared with those in the clinically normal group.