Antibody moieties within circulating immune complexes in heart transplant recipients

Circulating immune complexes were isolated from the sera of cardiac allograft recipients by bovine conglutinin/anti-conglutinin co-precipitation, or by gel filtration and protein A-Sepharose affinity chromatography. The antibody moieties within these isolated immune complexes were tested for specificity against heterologous anti-thymocyte globulins by solid phase radioimmunoassay, and bacterial and viral antigens by indirect immunofluorescence. The results showed that in addition to possessing specific anti-equine anti-thymocyte globulin antibodies, immune complexes also contained cross-reacting antibodies to rabbit anti-thymocyte globulin and vice versa, despite the patients only having received antibody of one species. Similarly, antibodies directed against bacteria or viruses (cytomegalovirus, Herpes simplex, virus, Epstein-Barr virus) were found within immune complexes obtained during overt infection, but also where infection was not detected. These results demonstrate the heterogeneous nature of immune complexes in heart transplant sera, and suggest that various stimuli, including ATG therapy, infection and possibly polyclonal B cell activation, may be involved in their generation in cardiac transplantation.