Stephen J. Prowse

Role of Lymphokine and Antigen in the Control of Specific T Cell Responses

Our interest in the process of T cell activation derives from a more general concern with the mechanism of the allograft reaction. In this review we will show how the study of allogeneic interactions led to the development of a two-signal model for T cell activation, in which both antigen and a hormone-like molecule produced by lymphoreticular cells (lymphokine) are seen to play an equally important role in the process of T cell activation. We will then go on to consider experimental evidence that supports the model, and to examine cellular requirements for the production and release of lymphokine from lymphoreticular cells.

Islet allografts are destroyed by disease occurrence in the spontaneously diabetic BB rat.

Transplantation of cultured islet and pituitary tissue from PVG (RT1C) donors to major histocompatibility complex-incompatible BB/D recipients (RT1U) results in tissue-specific destruction of the grafted islets but not of the pituitary. We interpret this response as disease occurrence in the MHC-incompatible islet graft. Islet damage is associated with eosinophil and mast cell accumulation in and around the grafted tissue. Antibody deposition is also present in tissues of the BB rat. This is suggestive of an antibody-mediated allergic reaction.

Desferrioxamine Treatment Prevents Chronic Islet Allograft Damage

BALB/cByJ islet allografts are acutely rejected when transplanted into allogeneic mice (CBA/J). Culture of the tissue for 7 days in 95% O2 before grafting is a suboptimal treatment for the reduction of immunogenicity in this strain combination. Approximately half the animals reject these transplants in a chronic fashion. Chronic islet rejection differs from acute rejection of uncultured allogeneic islets. During chronic rejection, beta cells within the transplanted tissue degranulate but remain intact when the animal returns to the diabetic condition. Acute islet rejection is characterized by the destruction of beta cells that remain heavily granulated as long as they remain intact. We examined the effect of the iron chelating agent, desferrioxamine, on chronic islet allograft damage. Desferrioxamine inhibited chronic islet allograft damage but did not influence the process of rejection of uncultured islet tissue. This effect of desferrioxamine could not be attributed to a direct immunosuppressive effect of this agent.

Interleukin 2 Production by Both Ly2+ and Ly2− T-Cell Subsets

Homogeneous T‐Cell populations produced by activating lymphocytes to I‐. K‐, or K+D‐region‐encoded determinants of the mouse H‐2 complex release interleukin 2 when restimulated by concanavalin A. Contrary to earlier reports on the cellular origin of the lymphokine, we find that interleukin 2 production can be either Ly2+ or Ly2− T‐cell‐dependent.

Cultured thyroid allografts induce a state of partial tolerance in adult recipient mice.

Thyroid allografts (BALB)c) prepared for transplantation by cyclophosphamide pretreatment of the donor, followed by organ culture of donor tissues for 3 weeks in a gas phase of 95% O2-5% CO2 function in normal CBA recipient mice for ≥ 350 days. Up to 100 days post-transplantation, the tissue can be rejected by challenge of the recipient with 105 BALB/c peritoneal cells. After prolonged residence in the recipient (>100, ≤350 days), only a proportion of allografts are rejected when the recipient is challenged with 105 followed by 106 peritoneal cells of donor origin. Recipients of long-term allografts are partially tolerant of BALB/c tissues. They are hyporesponsive to in vivo challenge with BALB/c spleen cells. However, lymph node cells from these animals respond essentially normally to stimulation with BALB/c spleen cells in vitro. Tolerant recipients will accept a second uncultured BALB/c allograft after a transitory rejection crisis. This crisis is not observed in the primary allograft.

The Reversal of Diabetes by Pancreatic Islet Transplantation

In this paper the theoretical basis of aiioreactivity and its relevance to transplantation biology is discussed prior to a review of work showing that culture of adult mouse pancreatic islets for 7 days in 95% O2 and 5% CO2 facilitates successful grafting to nonimmunosuppressed allogeneic recipients. These allografts function by reversing both chemically induced and spontaneous diabetes. The fetal mouse pancreas is more immunogenic than adult islets, and even after a culture period of 10 days in 95% O2 and 5% CO2, BALB/c allografts are consistently rejected by nonimmunosuppressed recipient mice. The immunogenicity of fetal pancreas is thought to be due to the presence of contaminating lymphoreticular celis in the mesentery surrounding the fetal pancreas. Digestion of the fetal pancreas with coilagenase allows the isolation of proislets that develop into functional islet tissue on transplantation. Fetal proislets are less immunogeneic than the whole fetal pancreas and may provide a source of tissue for clinical transplantation. Established islet allografts are relatively stable and are not rejected following nonspecific stimulation of the recipients immune system or following passive transfer of either antibody or antibody and complement. After prolonged residence in the recipient a state of a I log raft tolerance develops and such grafts resist rejection by specific stimulation of the recipient. The administration of donor antigen in the form of uvirradiated cells enforces this state of eliografi tolerance.

The Allograft Response

The allograft response is a response by host T lymphocytes reacting to transplantation antigens that are carried on allogeneic lymphoreticuler cells. In vivo this response usually leads to graft rejection. It is possible to circumvent this response by the elimination of the lymphoreticular cells from the grafts prior to transplantation. The paradox of the strong response to transplantation antigen on lymphoreticular cells and the weak response to the same antigen on graft parenchymal cells can be explained by the signaling requirements for T lymphocyte activation.

Reversal of Diabetes in Outbred Mice by Islet Allotransplantation

The combination of donor pretreatment with cyclophosphamide, organ culture in 95% O2:5% CO2 for 7–10 days, and short-term immunosuppression of recipients with cyclosporin A (CsA) were necessary to obtain 100% survival of single-cluster BALB/c islet allografts in outbred mice. In vivo and in vitro pretreatment of the donor tissue alone resulted in the acceptance of 45% of the islet allografts in nonimmunosuppressed outbred mice. CsA treatment of recipients alone yielded 40% survival of the untreated allografts. CsA treatment played an important role in maintaining the capacity of islet allografts to function in outbred mice. During CsA treatment, 88% of streptozocin-treated mice showed graft-dependent reversal of diabetes; the remainder showed no evidence of graft function, and CsA treatment failed to prevent acute graft rejection. After withdrawal of CsA immunosuppression, 38% of this total group remained normoglycemic. These findings suggest that modulation of both donor-tissue immunogenicity and recipient responsiveness will be required for successful pancreatic islet transplantation in diabetic humans.

Pancreatic islet allograft function in nonimmunosuppressed conscious mice.

CBA/H (H-2k) male mice were made diabetic by giving Streptozotocin 300 mg/kg intravenously. They were transplanted beneath the renal capsule with seven clusters of BALB/c (H-2d) adult islets, cultured for seven days in 95% O2 and 5% CO2. Basal blood glucose and weight gain returned to normal within 7 to 10 days. Blood glucose and serum insulin responses to intragastric glucose, intraperitoneal arginine and intraperitoneal theophylline were assessed after restoration of normoglycemia and compared with the responses in a control group of CBA mice. The animals were pretreated with intraperitoneal phentolamine and propranolol to reduce the stress of these procedures. Essentially normal carbohydrate tolerance was maintained in the transplanted animals but the insulin responses were markedly reduced, suggesting an increased sensitivity to insulin. The insulin content of the grafted tissue was also found to be considerably lower than that in the normal pancreas. This study demonstrates that in the mouse, adult pancreatic islet allografts can respond to stimuli that require functional adaptation by the islets. Further studies are required in larger animals before islet transplantation can be applied to the management of insulin dependent diabetic patients.

T LYMPHOCYTE FUNCTION IN VIVO: AMBIVALENCE OF THE CLASS I MHC ANTIGEN-REACTIVE SUBSET

Lymphocytes that recognize class I alloantigens (class I T cells) are able to lyse appropriate target cells and release lymphokines in vitro. However the relative contribution of these activities to biological, in vivo functions of these cells is unclear. It is possible to discriminate between these activities using cyclosporine (CsA).3 CsA inhibits lymphokine release from class I T cells but has no effect on their cytotoxic activity. The in vivo function of class I T cells is analyzed using 2 models; the local GVHR induced by the transfer of sensitized T cells to the foot-pad and islet allograft rejection induced by the passive transfer of sensitized T cells. Both reactions may be mediated by class I T cells. CsA inhibits the in vivo functions of the class I T cells in both systems—hence, these functions appear to be lymphokine-dependent. This demonstrates the ambivalence of this T cell subset in relation to biological function; the cells express direct cytotoxic activity and producing lymphokines. The alloreactivity of the class I T cells is dependent upon the latter activity.