The mechanism of action of anti-lymphocyte serum. Studies of antibody eluate

Intrathymic inoculation of donor bone marrow induces long-term acceptance of lung allografts

BACKGROUND

We investigated whether intrathymic inoculation of donor bone marrow at the time of transplantation induced long-term acceptance of lung allografts.

METHODS

Four- to-six-week-old August Copenhagen Irish (ACI) and Wistar Furth (WF) rats were used as donors and recipients, respectively. After being inoculated intrathymically with either donor-specific (ACI) or third-party (F344) bone marrow (2.0 x 10(7) cells/lobe), the recipient (WF) animal received a left lung transplant from an ACI donor. A short course of tacrolimus (1 mg/kg per day for 5 days) was administered. Animals were sacrificed at timed intervals after transplantation, and rejection was graded on a scale of 0 (none) to 4 (severe).

RESULTS

At 28 days, animals receiving donor-specific bone marrow have lower (p < 0.01) median rejection grade (MRG = 0.25; n = 6) than those receiving third-party bone marrow (MRG = 3; n = 6) and controls (no bone marrow; MRG = 2.5; n = 6). Animals receiving intrathymic donor bone marrow accepted lung allografts up to 380 days with minimal rejection (MRG = 2; n = 6). Long-term lung recipients also accepted a challenging donor-specific heart graft (n = 4) for more than 150 days. In mixed lymphocyte reaction assays, T lymphocytes of WF recipients that had received intrathymic bone marrow (from ACI donor) exhibited low response (similar to self antigens) to donor (ACI) cells, but reacted strongly (five times higher) to third-party (F344) cells.

CONCLUSIONS

Intrathymic inoculation of donor bone marrow at the time of transplantation along with a short course of tacrolimus induces long-term acceptance of lung allografts in rats. This simple approach of tolerance induction may have clinical application.

Mechanisms involved in antithymocyte globulin immunosuppressive activity in a nonhuman primate model

BACKGROUND

The mechanisms of action of polyclonal antithymocyte globulins (ATGs) are still poorly understood and the selection of doses used in different clinical applications (prevention or treatment of acute rejection in organ allografts, treatment of graft-versus-host disease, or conditioning for allogeneic stem cell transplantation) remains empirical. Low T-cell counts are usually achieved in peripheral blood during ATG treatment but the extent of T-cell depletion in lymphoid tissues is unknown.

METHODS

Experiments were conducted in cynomolgus monkeys using Thymoglobuline at low (1 mg/kg), high (5 mg/kg), and very high (20 mg/kg) doses.

RESULTS

ATG treatment induced a dose-dependent lymphocytopenia in the blood and a dose-dependent T-cell depletion in spleen and lymph nodes but not in the thymus, indicating a limited access of ATG to this organ. T-cell apoptosis in peripheral lymphoid tissues was the main mechanism of depletion. Remaining T cells in peripheral lymphoid organs were coated by antibodies and had down-modulated surface expression of CD2, CD3, CD4, and CD8 molecules, whereas their responsiveness in mixed leukocyte reaction was impaired. The survival of MHC-mismatched skin and heart allografts was prolonged in a dose-dependent fashion, despite the occurrence of a strong anti-ATG antibody response resulting in the rapid clearance of circulating ATGs.

CONCLUSION

The results indicate that T-cell depletion is achieved rapidly and primarily in peripheral lymphoid tissues at high ATG dosage. Short ATG treatments could therefore be clinically evaluated when major peripheral T-cell depletion is required.

Partial T-cell activation and anergy induction by polyclonal antithymocyte globulin

BACKGROUND

Polyclonal antithymocyte globulins have been assumed to deplete or sequester immunocompetent T cells. We investigated the hypothesis that anti-human thymocyte globulin (ATGAM)-mediated immunosuppression is delivered via nondepletive, immunologically specific actions as a consequence of simultaneous engagement of multiple T cell receptors.

METHODS

Purified T cells obtained from healthy volunteers or renal transplant recipients receiving their first dose of ATGAM were evaluated for proliferative responses and cell-mediated lympholysis. ATGAM binding and receptor expression were determined by flow cytometry. Cytokines and ATGAM levels were measured by enzyme-linked immunosorbent assay.

RESULTS

ATGAM-treated T cells showed significant dose-dependent inhibition of proliferation in vitro at concentrations comparable to those measured in patients. Effectors raised after ATGAM treatment failed to develop cytotoxicity. Supernatant interleukin (IL)-2 levels in ATGAM-treated cultures were significantly reduced (P<0.01 vs. control). IL-4 was not significantly altered. In vivo studies confirmed significant ATGAM-mediated inhibition of proliferative responses. Concanavalin A and OKT3-driven proliferation were reduced 30-60% by ATGAM. Flow cytometry showed that ATGAM recognized multiple cell surface receptors and resulted in markedly increased IL-2R and CD28 expression in the absence of proliferation, demonstrating partial T-cell activation. ATGAM synergized with phorbol myristate acetate to produce strong proliferation, which suggests that it provides a calcium-based signal resulting in anergy.

CONCLUSIONS

ATGAM recognizes and cross-links multiple cell surface receptors and costimulator molecules on human T cells. Simultaneous engagement by ATGAM in the context of allogeneic or mitogenic stimulation leads to partial T-cell activation and anergy.

Depletion of lymphoid tissues by tilorone. Ultrastructure and synergistic interaction with antilymphocyte serum

Antilymphocyte serum (ALS) caused lymphocyte depletion and shrinkage of thymus-dependent areas in spleen and lymph nodes of rats. Tilorone also depleted T lymphocytes, but light- and electron-microscopic examination revealed hyperplasia and vacuolation of the interdigitating cells that remained in the thymus-dependent areas, rather than shrinkage. These changes were not mediated by the adrenal gland. The combination of agents had a synergistic effect on the thymus-dependent areas in the spleen, lymph nodes, Peyer's patches, and bronchial-associated lymphoid tissue, all of which were severely depleted but maintained their normal dimensions. The combination of ALS and a tilorone analog that was capable of depleting lymph node but not spleen, gave a synergistic effect only in lymph node and not in spleen. Tilorone effects were transient, whereas ALS produced a long-lasting depletion. Administration of the two drugs at different times were synergistic only during the brief period of tilorone's effectiveness. The synergistic effects on T lymphocytes correlated well with immunosuppressive potency of the combined drugs on a T-lymphocyte-mediated auto-immune disease.

Cytotoxic effect of anti-lymphocytic globulin on human lymphoid cells

The cytotoxic activity of two anti-lymphocytic globulin (ALG) preparations was investigated by measurement of 51Cr release from human peripheral blood mononuclear cells and tonsil lymphocytes incubated with ALG in the presence of complement. Both types of ALG had a greater complement-dependent cytotoxic effect on tonsil lymphocytes than on peripheral blood mononuclear cells. The ALG preparations were more cytotoxic for a population of tonsil lymphocytes enriched in non-T cells than for one enriched in T cells. This finding does not support the view that ALG has a selective action on T lymphocytes.

The combined use of antilymphocyte serum and cyclophosphamide to suppress renal allograft rejection in the rat

Cyclophosphamide and antilymphocyte serum (ALS) were compared for their ability to suppress renal allograft rejection in the rat. These two agents were chosen since they are generally considered to act on different arms of the immune response, and might therefore complement each other's action. Dose response studies showed that both agents could suppress rejection completely. There were no differences in their ability to suppress the lymphocytotoxic antibody response to the graft and the histological patterns of rejection were similar. There was no evidence that cyclo-phosphamide was more effective in suppressing vascular lesions. The doses of both agents which suppressed the lymphocytotoxic antibody response were substantially lower than those required to suppress graft rejection. When suboptimal doses of the two agents were administered together, the combinations were found to be additive and not synergistic.

Acid elution of blood group antibodies from intact erythrocytes

Human IgM and IgG antibodies against blood group antigens (A, B, D, C, c, E, e, Fya, K), autoantibodies and mouse IgM and IgG antibodies against sheep erythrocytes have been eluted from intact human and sheep red cells by glycine-HCl buffer, pH 3.0. The yield of human antibodies was higher with acid than with heat and ether elution, and the contamination of hemoglobin in the eluate was negligible. The acid elution method is very simple and rapid and, therefore, highly suitable for experimental as well as routine immunohematological work.

Cumulation and elimination of horse-anti-dog lymphocyte and normal horse gammaglobulin in dogs

Two groups of dogs received daily intravenous doses of 20 mg/kg 131-I-labelled horse-anti-dog lymphocyte globulin or normal horse gammaglobulin respectively over a period of 11 days. Horse-anti-dog lymphocyte globulin showed a significantly higher eleimination rate than normal horse gammaglobulin. In contrary to the continuous increase in serum radioactivity during normal horse gammaglobulin treatment, there was a plateau after the 5th day in the horse-anti-dog lymphocyte globulin group. The xenogeneic protein concentration, measured with the single radial immunodiffusion technique, at the end of treatment was 165 +/- 8 mg/1 in the horse-anti-dog lymphocyte globulin, compared to 498 +/- 15 mg/1 in the normal horse gammaglobulin group. After treatment horse-anti-dog-lymphocyte globulin treated animals showed a significantly higher increase in active hemagglutination titer against horse erythrocytes with an average of 2(-8).

[Immune status of indefinitely surviving rat renal allograft recipients after short course of ALS-treatment Detection of a serum blocking factor by allorosette formation inhibition test (author's transl)]

53 LBNF1 kidneys were grafted into L-rats. 24 untreated recipients served as control and survived 16.1 +/- 1.7 days. 14 recipients were treated with 4 ml alloantiserum (ADS) each, and the other 15 animals with 4 ml ALS each. 9 and 10 of these 14 and 15 animals survived for more than 4 months. We performed GvH-reaction with spleen cells of these 19 animals. It showed normal cellular immune response. After splenectomy first donor specific skin was transplanted, 18 days later second skin of same origin (LBNF1) and 18' days after third party skin (LBufF1). The first grafts survived 13.1 +/- 1.9 days in the recipients of ADS treatment and 12.2 +/- 1.2 days in the recipients of ALS. Second skin grafts were rejected delayed in the former recipients as the first grafts, in the later more accelerated than the first grafts. The third grafts survived as the controls. Before and after skin grafting we could not detect lymphocytotoxin and hemagglutinin. The sera of animals with ADS therapy inhibited the spontaneous allorosette formation to 46.0 +/- 4.4% and of ALS therapy 37.7 +/- 9.2%. Our results suggest that after ALS treatment blocking antibodies were produced in the recipients and they cause the enhancement of kidney allograft.

Inhibition of T-cell differentiation by an antibody to a soluble thymic factor

An antiserum to chicken soluble thymic factor (STF) was prepared in rabbits and absorbed with chicken thymocytes until it reacted only with thymic reticuloepithelial cells. When injected into 6-day-old embryonated eggs, this antiserum caused a severe depletion of small lymphocytes in the cortical region of the thymus which was filled with large undifferentiated cells. In addition, reticuloepithelial cells displayed a marked disruption of cytoplasmic elements. The percentage of thymic lymphocytes bearing the T antigen was greatly reduced. It is believed that a factor responsible for differentiation of stem cells into T cells has been inhibited.

Antilymphocyte antibody purified by immunoabsorption and elution

A comparison has been made of several techniques for the preparation from antilymphocyte serum of pure antilymphocyte antibody by absorption on, and elution from mouse thymocytes. The best yield was obtained by a batch method using cells fixed in 0·1% formaldehyde as immunoabsorbent followed by elution with 0·12 M citrate buffer at pH 3·0. The antilymphocyte activity of eluates was studied in vitro by determination of membrane immunofluorescence titres and in vivo by the neutralization of the local renal xenogeneic graft-versus-host reaction. These tests showed that an IgG eluate of a rabbit antilymphocyte serum was nineteen times more active than the same weight of the whole IgG present in the parent serum.

Anatomical distribution of T and B lymphocytes in the rat. Development of lymphocyte-specific antisera

A method is described whereby antisera raised in rabbits to rat thoracic duct lymphocytes were made specific for the plasma membrane antigens of T and B lymphocytes. These lymphocyte-specific antisera were used in immunofluorescence assays to study the distribution of B and T cells in lymphocyte containing tissues and body fluids of the rat. Rabbit antirat B-cell serum (ALS(B)) reacted selectively with the surfaces of lymphocytes in the lymphoid follicles of lymph node cortex and in the follicles and marginal zones of splenic white pulp, but not with the surfaces of germinal center cells or plasma cells. An identical pattern of fluorescent staining was obtained with rabbit antirat Ig serum. It was shown by blocking, absorption, and immunoprecipitation studies that ALS(B) was composed in large part of antibodies to rat Ig, but that it contained antibodies to other B-cell antigens as well. Rabbit antirat T-cell serum (ALS(T)) reacted selectively with the surfaces of lymphocytes in the paracortex of lymph node and in the periarteriolar sheath of spleen, and with thymocytes. ALS(T) did not display anti-Ig activity. ALS(T) reacted with approximately 100% thymocytes and with 90% thoracic duct, 80% lymph node, 60% blood, 50% spleen, and 10% bone marrow lymphocytes in suspensions of cells from these sources. ALS(B) reacted with the remainder of the lymphocytes in the suspensions, except for bone marrow in which only 59% of lymphocytes had detectable B- or T-cell surface antigens. The population of T lymphocytes in rat bone marrow was depleted by drainage of lymphocytes from a thoracic duct fistula, thereby establishing their membership in the pool of recirculating T cells. Approximately 14% of lymphocytes issuing from the thoracic duct of TxBM donors reacted with ALS(T). The presence in these animals of a small number of T cells, calculated to be approximately 2% of the normal value, may account for the limited capacity of TxBM rats to respond to antigens that induce a cell-mediated immune response.

Regulation of the antibody response to type 3 pneumococcal polysaccharide. I. Nature of regulatory cells

The effect of treatment with antilymphocyte serum (ALS) on the magnitude of the plaque-forming cell (PFC) response to Type III pneumococcal polysaccharide (SSS-III) was assessed in athymic nude mice and thymus-bearing littermate controls. Without ALS treatment, the PFC response was slightly higher in nude than in control mice. Treatment with ALS had no effect on the response of nude mice; however, considerable enhancement was noted in thymus-bearing controls. Such enhancement was ALS dose-dependent and demonstrable under conditions in which there was substantial inactivation of thymic-derived "helper" cells required for an antibody response to erythrocyte antigens. These findings suggest that amplifier and suppressor cells, which have been reported to regulate the magnitude of the antibody response to SSS-III, represent populations of thymic-derived cells (T cells) that are not present in nude mice. The activities of "helper" T cells and regulatory T cells appear to be independent of one another and mediated by separate subpopulations of T cells.

Age-decrease of cells sensitive to an autoantibody-specific for thymocytes and thymus-dependent lymphocytes in NZB mice

NZB mice naturally produce an autoantibody which in the presence of complement is specifically cytotoxic for thymocytes and thymus-dependent lymphocytes (T-cells) in the peripheral lymphoid tissues (lymph nodes and spleen) and the circulation of mice. Using a direct cytotoxicity test with a NZB mouse serum pool which contained the high titred autoantibody, a progressive decrease was observed with age in the proportion of the autoantibody-sensitive cells in mesenteric lymph node, spleen, and blood of NZB mice in comparison with mice of other strains (C57BL/6J and NZW). The numerical decrease in the population of autoantibody-sensitive cells was evident at younger age and greater degree in the peripheral blood than in the lymph node and spleen. The age-decrease in the number of autoantibody-sensitive cells in lymph node and spleen contrasted with the numerical increase in nucleated cells in these organs. The age-decrease in the proportion and number of the autoantibody-sensitive cells in the blood exceeded the decrease in the blood lymphocyte count. This finding indicated that T-cells in the blood are selectively depleted with the ageing of NZB mice. A similar observation was made on the blood lymphocytes of (NZB × NZW)F₁ hybrid mice. The depletion of T-cells in the blood in association with the production of natural thymocytotoxic autoantibody is termed autoimmune thymus-dependent lymphocytopenia.

Evidence for a blood-thymus barrier using electron-opaque tracers

In order to verify the existence of a blood-thymus barrier to circulating macromolecules, the permeability of the vessels of the thymus was analyzed in young adult mice using electron opaque tracers of different molecular dimensions (horseradish peroxidase, cytochrome c, catalase, ferritin, colloidal lanthanum). Results show that although blood-borne macromolecules do penetrate the thymus, their parenchyma] distribution is limited to the medulla of the lobe by several factors: (a) the differential permeability of the various segments of the vascular tree; (b) the spatial segregation of these segments within the lobe; (c) the strategic location of parenchymal macrophages along the vessels. The cortex is exclusively supplied by capillaries, which have impermeable endothelial junctions. Although a small amount of tracer is transported by plasmalemmal vesicles through the capillary endothelium, this tracer is promptly sequestrated by macrophages stretched out in a continuous row along the cortical capillaries and it does not reach the intercellular clefts between cortical lymphocytes and reticular cells. The medulla contains all the leaky vessels, namely postcapillary venules and arterioles. Across the walls of the venules, large quantities of all injected tracers escape through the clefts between migrating lymphocytes and endothelial cells; also the arterioles have a small number of endothelial junctions which are permeable to peroxidase, but do not allow passage of tracers of higher molecular weight. The tracers released by the leaky vessels penetrate the intercellular clefts of the medulla, but they never reach the cortical parenchyma, even at long time intervals after the injection. Therefore, a blood-thymus barrier to circulating macromolecules does exist, but is limited to the cortex. Medullary lymphocytes are freely exposed to blood-borne substances.

Analysis of the biological activity of antilymphocyte serum. 3. Concentration of immunosuppressive activity in one IgG subfraction and its inhibition by another

Two IgG subfractions of horse antilymphocyte serum (ALS) were obtained by DEAE Sephadex chromatography. Although the fractions did not differ antigenically, they differed on amino acid and carbohydrate analysis, and in electrophoretic mobility. As demonstrated by binding studies, only the most positively charged population of IgG molecules (fraction 1) obtained from anti-lymphocyte serum had specificity for the small lymphocyte; 50 per cent of the molecules in this population bound specifically to lymphocytes in vitro. As determined by an in vitro correlate of immunosuppressive potency (rosette inhibition), fraction 1 (F₁) IgG from ALS contained approximately 4 times the specific activity of fraction 2 (F₂). F₁ was significantly more effective in prolonging skin graft survival than F₂, whereas F₂ contained the major component of the non-specific anti-inflammatory activity of serum. The anti-inflammatory effect was mediated by anticomplement activity.

F₂ was found to be an effective inhibitor of the immunosuppressive activity of F₁ both in vivo and in vitro. Quantitative studies indicated that 1 part of F₂ could maximally inhibit 4 parts of F₁. The percentage of F₂ present in serum IgG was inversely related to the skin graft survival elicited by the serum, which indicated that F₂ was active as an inhibitor when tested as purified fraction as well as in unfractionated serum. Following immunization when F₁ gained immunosuppressive potency, it lost non-specific anti-inflammatory activity. These observations indicated that not only was there a quantitative, as well as a qualitative concentration of immunosuppressive antibodies in F₁, but also that this activity was controlled by the concentration of F₂. This report, therefore, describes an IgG control mechanism which can limit the expression of antibody induced biological activity.

It is suggested that in ALS the immunosuppressive antibody molecules possess a greater net positive charge than the remaining population, and that this is due to the degree of the negative charge on the immunizing antigen. Using DEAE Sephadex chromatography, these populations could be separated into two differently charged populations of molecules, only one of which had significant immunosuppressive capability. This increase in activity resulted from the increase of specific molecules, the loss of non-specific molecules, and was manifest upon the removal of an IgG inhibitor.

Increased Incidence of Lymphoma in C3H/HeJ Adult Mice Injected with Gross Virus and Antithymocytic Serum

An increased incidence of lymphoma in adult C3H/HeJ mice injected with antithymocytic serum as compared with normal rabbit serum during a course of one to four weekly intraperitoneal injections of cell-free filtrates of Gross virus-induced lymphomas was noted. The latent period of lymphoma ranged from 119 to 298 days after initiation of treatment. The incidence tended to increase as the number of injections of cell-free filtrate was increased, with a maximum incidence reached at three injections.