Molecular interaction of growth hormone with two monoclonal antibodies recognizing distinct epitopes

Immune activation is required for the induction of liver allograft tolerance: implications for immunosuppressive therapy

Liver transplants in many animal models are unusual because often they are not rejected even when transplanted across complete major histocompatibility complex barriers without immunosuppression. Their paradoxical behavior is even more obvious when the immune mechanism of acceptance is examined. Instead of acceptance resulting from a lack of immune response to the graft, the opposite occurs, and there is an unusual extensive increase in immune activation in acceptance compared with rejection. This abnormal extensive immune activation is driven by donor leukocytes transferred with the liver and results in death of the recipient cells that would normally reject the transplant. Some forms of immunosuppression inhibit this activation-associated liver transplant tolerance. The significance of these findings and possible means to design future treatment protocols for clinical transplantation that optimize management of liver transplant recipients are discussed.

Evidence that apoptosis of activated T cells occurs in spontaneous tolerance of liver allografts and is blocked by manipulations which break tolerance

BACKGROUND

Fully allogeneic liver grafts from piebald virol glaxo to dark agouti rats are spontaneously tolerated, whereas kidney transplants between these strains are rejected. Liver tolerance is broken by donor irradiation or peritransplant corticosteroid treatment of recipient rats, both of which interfere with the activation of recipient cells.

METHODS

In this study we used a combination of immunohistochemical staining, reverse transcription-polymerase chain reaction, and terminal deoxynucleotide transferase-mediated dUTP nick end labeling and Annexin-V apoptosis assays to compare donor cell migration, cytokine profiles, and leukocyte apoptosis in grafts and lymphoid organs from tolerant liver and rejecting kidney recipients. We then examined the effect on apoptosis of treatments which abrogate liver tolerance.

RESULTS

Liver transplantation in this tolerant strain combination is accompanied by rapid migration of many passenger leukocytes to the recipient spleen and lymph node, concurrent with a marked but transient increase in the amount of mRNA for the cytokines interleukin-2 and interferon-gamma. Apoptotic cells appear promptly in the spleen, their numbers reaching a peak 2 days earlier than has been previously shown for the graft infiltrate. Both CD4+ and CD8+ T cells undergo apoptosis and apoptotic cells are most concentrated among CD25+ T cells. In contrast, renal transplant rejection is associated with limited donor cell migration to lymphoid tissues and significantly less up-regulation of interleukin-2 and interferon-gamma in the spleen. Few apoptotic cells are detected in spleen or graft infiltrate during rejection, whereas apoptotic renal tubular and glomerular cells are found from day 5. Either recipient steroid treatment or donor irradiation significantly reduced the number of apoptotic cells in liver graft infiltrates and recipient spleen.

CONCLUSIONS

Taken together, these findings suggest that a mechanism akin to activation-induced cell death, with apoptosis of alloreactive recipient cells may be responsible for the induction of spontaneous liver transplant tolerance.

A monoclonal antibody to oestradiol potentiates the stimulation of the specific activity of the brain type creatine kinase by oestrogen in vivo and in vitro

We described previously the in vivo immunoneutralization effects of a high affinity anti-oestradiol antibody clone 15 in blocking ovulation and synaptic remodeling in cycling female rats. In the present study we report the enhancing effects of this antibody. Treatment of ovariectomized female rats or female derived skeletal cell cultures in vitro with anti-E2 15 plus oestrogen (E2) potentiated the specific activity of the brain type creatine kinase (CK) response to E2 in the rat tissues or skeletal cells. The enhancing CK response of anti E2 15 plus E2 was time- and dose-dependent in the uterus, thymus, epiphysis and diaphysis of ovariectomized female rats. In the pituitary, on the other hand, anti-E2 15 blocked the stimulatory CK response to E2. Two other high affinity anti-E2 antibodies, clones 8D9 and 11B6, had no effect in augmenting the response of CK to E2 in rat tissues. Moreover, the enhancing CK response in rat tissues was specific to anti-E2 15 plus E2 since the intact anti-E2 in the presence of other oestrogen mimetics, such as oestriol or stilbestrol or tamoxifen did not potentiate the CK response in rat tissues. In this model system the Fab' monomer of anti-E2 15 abolished the CK response to E2 in rat tissues and not to anti-E2 15 plus E2 whereas tamoxifen completely blocked the CK response to anti E2 plus E2. Anti E2 15 may therefore serve as a specific carrier in delivering E2 to oestrogen sensitive rat tissues or cells containing functional oestrogen receptors and thereby increasing the magnitude of E2 effects in vivo and in vitro.