1. Sera from 11 highly sensitized multiparous dialysis patients were studied in order to define the target antigens, antibody class and relationship with paternal HLA class I antigens of the underlying lymphocytotoxic antibodies. All sera contained lymphocytotoxic antibodies to over 70% of a panel of lymphocytes from 24 donors (panel reactivity > 70%). 2. Inhibition of cytotoxic activity against paternal lymphocytes by monoclonal antibodies to HLA framework determinants indicated that all 11 sera contained lymphocytotoxic antibodies to paternal class I antigens. In addition, five sera contained lymphocytotoxic antibodies to paternal class II antigens. 3. In order to determine the extent to which lymphocytotoxic antibodies were directed to paternal antigens, the panel reactivity of sera was compared before and after absorption with paternal peripheral blood lymphocytes. Over 50% of panel reactivity was absorbed from eight out of 11 sera, and in three of these 11 over 80% was absorbed. In the majority of patients this change in panel reactivity could be ascribed to binding of lymphocytotoxic antibodies to specific paternal class I antigens. 4. Digestion of sera with dithiothreitol had no significant effect on panel reactivity, indicating that the lymphocytotoxic antibodies were of immunoglobulin G class. 5. No sera reacted with either autologous lymphocytes or K562 cells, indicating an absence of autoantibodies. 6. These studies imply that panel-reactive lymphocytotoxic antibodies in the sera of highly sensitized multiparous patients are those which mediate hyperacute renal allograft rejection. Their development may be related to secondary humoral responses to angtigens in blood transfusions from donors who share paternal class I specificities.

1. Blood transfusions improve renal allograft survival rates, but may induce antibodies which are directed to class I major histocompatibility complex antigens and mediate hyperacute transplant rejection. A model to study the development of such antibodies was developed in inbred strains of rats. 2. The influence of transplantation antigens shared between an initial course of blood transfusions, given with cyclosporin A, and a subsequent antigenic challenge (blood transfusion), given without cyclosporin A, on alloantibody responses to class I major histocompatibility complex antigens was then investigated. 3. Cyclosporin A administration prevented the development of alloantibodies to class I major histocompatibility complex antigens during the initial transfusion period. 4. After the challenge transfusions, alloantibody responses to class 1 major histocompatibility complex antigens were suppressed when class I major histocompatibility complex or minor histocompatibility antigens were shared between the initial and final transfusions. 5. This suppression only extended to third party class I antigens when minor histocompatibility complex antigens were shared between the initial and final transfusions. Sharing of class I or class II antigens had no effect on alloantibody responses to third party class I antigens co-expressed on the same cell. 6. These studies suggest that cyclosporin A given with blood transfusions may prevent clinical sensitization while permitting the development of suppressor activity, mediated by shared minor histocompatibility complex determinants, to a broad range of potential donor antigens.

1. Humoral immune responses to allogeneic blood transfusions and semi-allogeneic pregnancies were monitored by the indirect haemagglutination assay in strains of inbred rats. 2. Similar titres and ranges of cross-reactive allo-antibodies were induced by blood transfusions and pregnancy; the maternal alloantibody response to paternal antigens was not increased by an unrelated antigenic stimulus. 3. Immunosuppression with cyclosporin, A was effective in preventing the primary humoral immune response produced by blood transfusion but not in abrogating the established immune response to previous pregnancy. 4. These studies have established an animal model of sensitization that both stimulates, the clinical situation of many potential renal transplant recipients and permits analyses of the different antigenic stimuli involved.

1. The immunological mechanisms involved in sustaining normal semi-allogeneic pregnancies and in the enhancement of organ allografts were investigated in inbred rats. 2. The antigenic targets for alloantibodies formed after leucocyte transfusions and multiple allogeneic pregnancies were defined by the EA rosette inhibition (EAI) assay in several congenic and recombinant inbred rat strains. 3. Alloantibodies produced by leucocyte immunization (conventionally induced antisera) were directed only to RT1-encoded (major histocompatibility complex, MHC) antigens. Both RT1A (class I MHC) and either RT1B, D (class II MHC) or RT1C (Qa-like) antigens were targets for these alloantibodies; responses to the latter three antigens could not be separated with available congenic recombinant inbred rat strains. 4. Alloantibodies produced as a consequence of multiple semi-allogeneic pregnancies (pregnancy-induced antisera) were directed only to RT1A antigens. 5. Allogeneic pregnancies in which the paternal strain differed from the maternal strain only at the RT1A gene locus produced suppression of a subsequent maternal immune response.

1. Uraemic rats maintained on either a high or a low phosphate diet for 12 weeks were allocated to one of the following oral vitamin D treatment groups and received: (a) 1,25-dihydroxycholecalciferol [1,25-(OH) 2 D 3 ], (b) 24,25-dihydroxycholecalciferol [24,25-(OH) 2 D 3 ], (c) both 1,25-(OH) 2 D 3 and 24,25-(OH) 2 D 3 , or (d) no vitamin D supplements. 2. Mean serum creatinine concentrations were elevated to a similar extent in all groups. Mean serum concentrations of calcium, phosphate and alkaline phosphatase were not significantly different from normal in any of the groups. 3. In the group receiving the high phosphate diet and no vitamin D supplements, calcified bone area measured by quantitative computerized histomorphometry was significantly lower than in (i) the group receiving the low phosphate diet and no vitamin D supplements (0.01 > P > 0.001), and in (ii) the groups receiving high phosphate diet and either 1,25-(OH) 2 D 3 (0.01 > P > 0.001) or 24,25-(OH) 2 D 3 (0.01 > P > 0.001). 4. We conclude that (i) uraemic rats maintained on a high phosphate diet for 12 weeks develop skeletal demineralization, (ii) this process does not occur in rats on a low phosphate diet, and (iii) a decrease in calcified bone area may be prevented by treatment with either 1,25-(OH) 2 D 3 or 24,25-(OH) 2 D 3 .

1. The influence of allogeneic pregnancies on the survival of subsequent rat renal allografts was investigated in three rat strain combinations. 2. Multiple but not single pregnancies produced significantly more long-term surviving kidney grafts than were found in virgin animals; the effect was specific for paternal antigens, as multiple pregnancies by an unrelated strain did not prolong kidney graft survival. 3. In the multiparous groups, those animals with long-surviving grafts had significantly higher levels of non-cytotoxic antibodies against paternal strain B-lymphocytes (detected by the erythrocyte antibody rosette inhibition assay) than did animals which rejected their grafts. 4. The results show that multiple pregnancies may produce a state of specific unresponsiveness to paternal antigens, similar to enhancement, which is marked by the presence of non-cytotoxic antibodies against paternal B-lymphocytes. It is suggested, therefore, that enhancement may be one of the protective mechanisms which prevent rejection of the fetus during pregnancy.

1. Peak 47 Ca absorption and 7 day 47 Ca retention were measured by a whole-body radioactivity counting technique in 10 haemodialysis patients before and after treatment with 1,25-dihydroxycholecalciferol [1,25-(OH) 2 D 3 ] and 24,25-dihydroxycholecalciferol [24,25-(OH) 2 D 3 ]. 2. Before treatment all patients had low peak 47 Ca absorption and 7 day 47 Ca retention. 3. After treatment with 1,25-(OH) 2 D 3 (0.25-1 μg/day for 4–12 months) peak 47 Ca absorption and 7 day 47 Ca retention returned to normal. 4. After treatment with 24,25-(OH) 2 D 3 (2 μg/day for 4–12 months) peak 47 Ca absorption and 7 day 47 Ca retention remained at pre-treatment levels. 5. It is concluded that physiological doses of 24,25-(OH) 2 D 3 have no effect on calcium absorption or retention in uraemic man.