G. J. A. Clunie

AN EARLY PREGNANCY FACTOR DETECTED IN HUMAN SERUM BY THE ROSETTE INHIBITION TEST

Modification of maternal lymphocyte activity has been demonstrated early in pregnancy by the rosette inhibition test. Normal human lymphocytes showed a similar depression of activity after incubation in serum from pregnant women, indicating that the response was caused by a serum factor. This early pregnancy factor has been differentiated from other substances which appear later in pregnancy and which may also be involved in the suppression of the maternal response. The results of this investigation suggest that the early pregnancy factor may be necessary for the continued viability of the early embryo.

Early pregnancy factor is immunosuppressive

IMMUNOSUPPRESSION during pregnancy has important consequences not only with respect to the recognition of the antigenically dissimilar embryo1 but also in terms of susceptibility to viral or tumour assaults2,3. We have recently described an early pregnancy factor (EPF) detectable within 24 h of mating and have postulated that this protein is responsible for depression of lymphocyte activity during pregnancy4–6, Immunosuppressive properties have been attributed to other proteins detectable during pregnancy. These include pregnancy-associated macroglobulin7,8 α-fetoprotein9 and human chorionic gonadotropin (HCG)10,11. One characteristic these substances have in common, but in which they differ from EPF, is that they are not present, or not detectable, in the early stages of pregnancy. Recently the immunosuppressive activity of HCG has been disputed by several workers working with highly purified material12,13. We have now shown that EPF inhibits the expression of an immune response in vivo.

Studies of the rosette inhibition test in pregnant mice: evidence of immunosuppression?

The rosette inhibition test has been utilized as a measure of immunosuppression following organ transplantation, and we have recently demonstrated that it can also be used in detecting a state of depression of lymphocyte reactivity occurring in pregnant mice. If the depression of lymphocyte reactivity provides an indication of immunosuppression, then this study has shown that, in the mouse, the spleen lymphocytes are immunosuppressed as early as 4 h after fertilization. This state persists for 13–15 days, with a return to normal 4–6 days before full term. A similar depression of normal spleen lymphocytes can be induced in vitro by incubating these lymphocytes with serum taken from pregnant mice 6 and 24 h after mating. The serum factor detected was shown to be stable when heated at 56 °C but not at 72 °C, and to be non-dialysable. It was detected in serum to a dilution of 1 in 64. Further work is being undertaken to investigate this phenomenon and to pursue the purification and identification of the pregnancy factor.

T SUPPRESSOR CELLS INDUCED BY TRANSFUSIONS AND CYCLOSPORINE : STUDIES IN THE MURINE CARDIAC ALLOGRAFT MODEL

Pregraft transfusion combined with immunosuppression at the time of grafting improves the survival of clinical and experimental allografts. The mechanisms responsible for this effect were investigated in the murine model of cardiac transplantation, combining transfusions 7 to 30 days prior to transplantation with cyclosporine 100 mg/kg, 7 to 20 days pregraft or on days 0, 4, and 6 after grafting. Pregraft DST, third-party blood, and CsA all improved graft survival in the BALB/c-to-CBA donor-recipient combination. In animals treated with DST at 14 days pregrafting, 4/9 grafts survived for greater than 100 days. In those given C57BL/6 blood, or CsA on days 0, 4, 6 postgraft, 1/9 grafts survived for greater than 100 days. When 10(7) spleen cells from DST-treated CBA mice with long-surviving BALB/c heart grafts were transferred to naive CBA mice that then received a BALB/c heart 24 hr later, the transferred cells prolonged graft survival, with all grafts functioning at greater than 40 days, and 4/7 at greater than 100 days. Selective removal of T cells from the spleen cell population prior to transfer showed that L3T4+ T cells, but not Ly-2+ T cells, were required to maintain BALB/c allografts. Combining a short course of CsA with DST was more effective than either treatment alone. The most effective combined treatment was DST at day -14 with 100 mg/kg CsA given on days 0, 4, and 6 postgrafting (8/10 grafts survived greater than 100 days). This treatment also induced splenic suppressor T cells of the L3T4+ Ly-2- phenotype. These results clearly show that L3T4+ splenic T suppressor cells are induced by donor-specific blood transfusion with or without CsA treatment, and that these cells play a role in maintaining long-term tolerance to allografts in the mouse heart transplant model.

Adverse influence of recipient lymphoid resistance to in vitro immunosuppression on the outcome of kidney transplants.

The study investigated whether preoperative in vitro sensitivity of lymphocytes from potential renal transplant recipients could identify patients at increased risk of acute rejection following transplantation and immunosuppression with cyclosporine, azathioprine, and prednisolone. Mixed lymphocyte culture responses were measured preoperatively in the presence of methylprednisolone, CsA, and antithymocyte globulin, and without immunosuppressive agents in 50 transfused recipients of primary cadaver renal transplants. Patients were classified as sensitive if all three immunosuppressive agents produced more than 50% inhibition of their MLC responses, and as resistant if one or more agents failed to produce 50% inhibition. All patients received postoperatively a standardized triple immunosuppressive regimen. Acute rejection was confirmed histologically and treated with Pred with or without ATG or monoclonal antibody OKT3. A total of 29 patients (58%) were sensitive and 21 (42%) were resistant; 4 patients were resistant to 3 agents, 5 were resistant to MP and ATG, 6 were resistant to MP and CsA, and 6 were resistant to MP alone. Sensitive and resistant groups did not differ in age, sex, transfusion history, HLA A, B and DR mismatches or duration of follow-up. The resistant group had a higher rate of graft loss from acute rejection (chi 2 = 6.0, d.f. = 1, P less than 0.02), more episodes of acute rejection (chi 2 = 8.7, d.f. = 3, P less than 0.05), and a higher proportion of patients in whom reflux nephropathy was the cause of renal failure (chi 2 = 18.3, d.f. = 1, P less than 0.001). The resistant group also had a higher proportion of highly sensitized patients and higher serum creatinine concentrations than the sensitive group, although the differences did not reach statistical significance. The study indicates that patients at high risk of acute rejection of renal allografts can be identified by a pretransplant in vitro assay, a finding that could influence recipient selection and immunosuppression.

Leucocyte migration inhibition test in cadaveric renal transplantation.

The leucocyte migration inhibition test has been studied in a series of 192 renal allograft recipients. Seventy-seven patients showed no evidence of inhibition in the early post-transplant course, but 31 of these demonstrated clinical evidence of rejection, a false-negative rate of 16%. The remaining 115 recipients all demonstrated inhibition, with 13 of these showing no clinical evidence of rejection, a false-positive rate of 6.7%. Early antirejection therapy on the basis of inhibition did not result in improved kidney survival when compared with those recipients who did not receive specific therapy until there was clinical evidence of rejection. The leucocyte migration inhibition test did not detect changes attributable to humoral factors, which probably accounts for the high false-negative rate, and has not proved to be sufficiently reliable to be of value clinically as a single test. A combination of tests designed to detect both humoral and cellular factors responsible for rejection deserves further study.