Influence of a DLE-extracted lymphocytic suppressor factor on CsA-induced immunosuppression.

From dialyzable leucocyte extracts (DLE) we have purified a hydrophilic low-mol. wt. factor (about 1 kDa) which we have named lymphocytic suppressor factor (LSF) as it is able to suppress antigen- and mitogen-induced lymphocyte transformation and to prolong allograft survival in C57b/6N mice (H-2b) transplanted with fully mismatched skin from C3H/HeN mice (H-2k). At the molecular level LSF acts by inhibiting DNA replicational and transcriptional processes in activated lymphocytes, isolated rat hepatocyte nuclei, and cell-free systems. Amino acid analysis indicates that LSF is a peptide composed of Asp, Glu, Ser, Thr, Ala, Gly, Arg and probably Met, with the N-terminus blocked, possibly by pyroglutamic acid. When combined "in vitro" with cyclosporine A (CsA), LSF increased about 20 times the potency of CsA in inducing suppression of mitogen-stimulated lymphocytes. In C57b/6N mice with skin graft from C3H/HeN mice and undergoing immunosuppression with CsA (50 mg/kg/day), the splenocyte LSF content increased about 5 times. However, LSF values returned to normal in mice recovering normal responsiveness due to progressive withdrawal of CsA. These data show that LSF has an important role in the development and maintenance of CsA-induced immunosuppression. We suggest that, by influencing DNA replicational and transcriptional processes of lymphocytes, LSF may play a role also in the onset and progression of AIDS induced by retroviruses.

Inhibition of in vitro adherence of antibody-coated red cells to monocytes by the dialyzable leukocyte extract.

The red cell-monocyte assay (RMA), which has been used to evaluate the clinical significance of red cell (RBC) antibodies, was employed to test the effect of the dialyzable leukocyte extract (DLE) on in vitro adherence to monocytes of human RBCs coated with alloantibodies or autoantibodies. The total association index (TAI) of the RMA, expressing the number of RBCs adhering to or phagocytosed by 100 monocytes, indicated a potent inhibitory activity of DLE in the test system. TAI values of 100.4 +/- 20.1 (mean +/- SD) in the control sample, consisting of RBCs coated in vitro with anti-D, dropped to 4.0 +/- 2.1 when DLE was present in the assay medium at a concentration of 0.5 U per mL. Similar results were obtained with RBCs coated with IgG antibodies in vivo. The inhibition was dose dependent and was associated with a thermolabile component of DLE. This study establishes that DLE can modulate monocyte function by inhibiting the recognition of IgG sensitized red cells.

Purification of immunomodulatory factors in human peripheral blood leukocytes.

Procedure is described for purifying low-molecular-weight factors with antigen-aspecific properties from a dialysate of human leukocyte extract. It includes gel chromatography on Sephadex G-25 and G-15, ion-exchange chromatography, reversed-phase high-performance liquid chromatography (HPLC) on a C18 hydrophobic column and gel permeation HPLC. The immunosuppressive factor (mol.wt. 800-1000) was purified to near homogeneity. It is probably of peptidic nature, although it is pronase resistant. The enhancer factor (mol.wt. 300-600) is eluted from chromatographic columns together with a hypoxanthine-like substance. Nevertheless, the biological activity cannot be attributed to the purine derivative. Identification of this amplifier activity is still lacking.

Functional C8 associated with human platelets.

Haemolytic assay for C8 revealed its association in functionally active form with washed human platelets. Platelet-bound C8 haemolytic activity was inhibited by F(ab')2 anti-C8 and was undetectable in the platelet suspension obtained from three C8 deficient patients. Incubation of platelets from C8 deficient individuals in normal plasma did not restore C8 haemolytic activity, indicating that platelets do not absorb C8 from plasma in vitro during platelet preparation. Thrombin, a mediator of the platelet release reaction, did not induce the release of C8 from normal platelets. Conversely, lysis of EAC1-7.9 by platelet bound C8 was not accompanied by release of beta-thromboglobulin or serotonin from the platelets. C8 was detected in a homogenate prepared from platelets as well as in the supernatant collected after high speed centrifugation of the homogenate. The association of C8 with platelets as an individual component rather than as part of the C5b-9 membrane-attack complex was supported by the following evidence: platelet bound C8 eluted from a Sephacryl S-200 column at the same volume as C8 from normal human serum; F(ab')2 anti-C8, but not F(ab')2 anti-C5, inhibited platelet C8 activity; the platelet homogenate, which lysed EAC1-7.9, had no effect on EAC43 which are susceptible to the lytic activity of the C5b-9 complex.

Blood transfusion and kidney transplantation: effect of small doses of blood on kidney graft function and survival.

A controlled clinical trial was started to evaluate whether small doses of blood given pretransplant determine a transfusion effect while reducing the risk of antibody production. For this purpose, 65 consecutive never transfused patients suffering from end-stage renal failure were assigned to one of two groups: the first group was transfused with 1 unit of packed red cells (containing a mean of 2350 x 10(6) leukocytes, 900 x 10(6) mononuclear cells) 3 times at 15-day intervals. The second group received one transfusion of about 30 ml of blood adjusted to contain 100 x 10(6) mononuclear cells. While no definitive conclusions are still possible, preliminary data indicate the following: (1) three small transfusions are capable of immunizing the recipient, but lymphocytotoxic antibodies tend to disappear rapidly; (2) in vitro lymphocyte response to lectins of patients receiving small transfusions is not significantly different from that of patients receiving standard transfusions; (3) the two groups of patients differ significantly as far as the T4+ /T8+ cell ratio is concerned: in fact while a decrease of the ratio is observed after standard transfusions, small transfusions determine an increase of the ratio, mainly due to a decrease in the number of T8+ cells; and (4) the clinical course and survival of the graft is worse in patients treated with small transfusions than in those treated with standard transfusions.

Study on the turnover of the receptor for the third component of complement on human lymphoid cells.

The in vitro turnover of the receptor for the third component of complement (C3) was studied in normal peripheral blood lymphocytes (PBL) and in lymphoblastoid cells from established cell cultures of both "normal" and "malignant" origin. The turnover was evaluated by studying i) the disappearance rate of the C3-receptor in cells in which the protein synthesis was blocked by cycloheximide and puromycin, ii) the reexpression rate of the C3-receptor after treatment of the cells with either rabbit antiserum against B lymphocytes or mouse C activated through the alternative pathway by inulin. The results show that the C3-receptor of all the lymphoid cells has roughly a half-life of about 3 to 4 hr. However, the cultured lymphoblastoid cells were less sensitive than normal PBL to inhibition by cycloheximide and showed a faster reexpression rate of the C3-receptor. A spontaneous release of the receptor was found to occur, since a receptor-like activity was detected in the spent culture medium of long-term cultured lymphoid cells.