Serial analysis of circulating immune complexes, complement, and antithymocyte globulin antibodies in heart transplant recipients.

Thirteen heart transplant patients receiving heterologous antithymocyte globulin were examined serially for the presence of circulating immune complexes, activation of complement, and antibodies to antithymocyte globulin. Using three independent assays, all patients were found to develop immune complexes at some time following transplantation, mostly as a consequence of antithymocyte globulin administration and infection. Simultaneous analysis of endogenous complement levels revealed C3 and C4 hypocomplementaemia in 28 and 44% of the samples, respectively. However, no correlation was evident between immune complex or complement levels and cardiac rejection assessed histologically in 64 endomyocardial biopsies. Serial analysis of antibodies to equine and rabbit antithymocyte globulin by solid-phase radioimmunoassay showed that 8 of 10 patients had significantly elevated values. Evidence was also obtained which indicated a substantial degree of cross-reactivity between the antibodies to these heterologous proteins. The results demonstrate a complex interplay of immune reactants relating to transplantation, infection, and immunosuppression therapy.