Development of a radioimmunoassay for the detection and quantitation of immune complexes in canine sera by solid phase C1q binding essay

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Staphylococcus aureus Cowan I strain (SAC) contains a cell wall protein which has an affinity for Innnune complexes and. the IgG of most mammalian species. Dogs with spontaneous mammary adenocarcinoma whose plasma was perfused over immobilized SAC developed a potent, apparently humorally-mediated tumoricidal response within hours after the perfusion. This response was accompanied by changes in the humoral concentrations of immune complexes, IgG, and tumor-specific antibodies. Prior to SAC perfusion, the plasma concentrations of immune complexes in the tumor-bearing animals were markedly increased over the levels found among the normal dogs. SAC efficiently removed the complexes from the plasma during the first 5-6 minutes of the perfusion, but as the perfusion continued, the concentration of complexes in plasma immediately leaving the SAC filter equalled or exceeded the preperfusion values. Following the perfusion, the in vivo quantities of circulating immune complexes were elevated, the total serum IgG concentrations were depressed temporarily but rapidly rebounded to greater than pre-perfusion values, and the levels of tumor-specific antibodies became increased and remained elevated for varying periods of time. For these studies, a solid phase C1q binding assay was shown to be reliable and reproducible in the quantitation of canine immune complexes. This assay may also be useful in the identification of dogs with tumors that are amenable to the extracorporeal SAC perfusion treatment.