An immunological study of renal allograft rejection using the direct macrophage inhibition test

The direct macrophage inhibition test was used to evaluate the relationship between cellular immune response and graft rejection in related renal allograft recipients. Forty recipients were evaluated before and at regular intervals after transplantation while on maintenance immunosuppressive therapy. Allograft recipients were classified into four categories: 1) Non-HL-A-identical with a rejection episode (14 patients); 2) non-HL-A-identical without a rejection episode (13 patients); 3) 3) HL-A-identical with a rejection episode (3 patients); 4) HL-A-identical without a rejection episode (10 patients). Ten HL-A-identical sibling pairs in good health were utilized as controls. Cellular immunity against donor antigen (macrophage inhibition greater than 20%) uniformly occurred in 16 of the 17 patients who experienced episodes of rejection in both the HL-A-identical and nonidentical graft recipient groups. Transplant recipients who did no experience any rejection episodes up to 2 years post-transplant, and members of the HL-A-identical control group had negative inhibition tests. In 5 cases changes in cellular immune response preceded rejection by several days. The two recipients with positive macrophage inhibition to their prospective donors before transplantation experienced irreversible accelerated rejection. Thus, the direct macrophage inhibition test can be used to screen prospective related donors and to monitor cellular immunity in recipients after transplantation. Preexistent cellular immunity to the donor detected before transplantation correlates with a very high incidence of rejection episodes. Graft recipients who experienced no rejection episodes failed to develop cellular immunity to their donors.