Induction of transplantation tolerance in rats by spleen allografts. II. Evidence that W3/25+ T suppressor/inducer and OX8+ T suppressor/effector cells are required to mediate specific unresponsiveness

Allochimeric class I MHC protein-induced tolerance by partial TCR engagement requires activation of both CTL4- and common gamma-chain-dependent cytokine signals

BACKGROUND

The various toxicities associated with the general immune suppression resulting from current clinical immunosuppressive therapies continue to plague transplant recipients as well as jeopardize allograft survival.

METHODS

The present study utilized allochimeric class I MHC antigens (alpha1hu70-77-RT1.Aa) bearing only four donor RT1.Au polymorphic amino acids (a.a.; His70, Val73, Asn74, and Asn77) superimposed on the recipient RT1.Aa background to induce transplantation tolerance in the rat cardiac transplant model.

RESULTS

Oral delivery of alpha1hu70-77-RT1.Aa protein alone (days 0-6) induced tolerance, as evidenced by inhibition of both acute and chronic rejection processes. Delivery of alpha1hu70-77-RT1.Aa with therapeutic doses of cyclosporine (CsA) also prevented chronic rejection, otherwise readily developed after treatment with CsA alone. A polymerase chain reaction (PCR)-based analysis showed that tolerant recipients had reduced numbers of interleukin (IL)-2/interferon (IFN)-gamma-producing T helper (Th)1 cells and elevated numbers of IL-4/IL-10-producing Th2 cells. Adoptive transfer experiments revealed that potent regulatory T cells mediated tolerance. The same T cells displayed diminished T cell receptor (TCR)-driven signaling via extracellular regulated kinase, AP-1, and NF-kappaB, as well as the common gamma-chain (gammac) cytokine-receptor-induced signaling by Janus kinase 3 (Jak3)/stimulators and activators of transcription Stat/5 pathways. Tolerance induction was prevented in vivo by inhibition of signal 2 by CTL4Ig or of signal 3 by either rapamycin, which disrupts the mammalian target of rapamycin, or AG490, which inhibits Jak3. Finally, partial or complete tyrosine phosphorylation of Zap70 was observed in alloantigen-specific T cell clones in response to tolerogenic versus immunogenic peptides, respectively.

CONCLUSIONS

Tolerance induction by allochimeric proteins is achieved by partial TCR activation in the presence of signals 2 and 3, resulting in a skewed Th2 phenotype.

Immunosuppression by inhibition of cellular adhesion mediated by leukocyte function-associated antigen-1/intercellular adhesion molecule-1 in murine cardiac transplantation

BACKGROUND

Donor alloantigen-specific tolerance to vascularized allografts can be induced by several treatments, but the immunological mechanism(s) of these effects remain unclear. One hypothesis is that allograft unresponsiveness is correlated with a shift in the pattern of expression of the T helper 1 versus T helper 2 T-cell cytokines. We report here an extensive analysis of murine cardiac allografts, during normal first set rejection and in mice treated with anti-adhesion molecule monoclonal antibodies (mAbs), a regimen that results in prolonged unresponsiveness.

METHODS

A combination of immunohistochemical staining with a panel of mAbs, and in situ hybridization with a panel of digoxigenin-labeled riboprobes, was performed on frozen-tissue sections of cardiac allografts.

RESULTS

In several strain combinations, injection of anti-leukocyte function-associated antigen-1 and anti-intercellular adhesion molecule-1, from day 0 to day 6 after transplantation, results in significant long-term survival. Examination of tolerated cardiac allografts by in situ hybridization and immunohistochemical staining shows an altered cytokine expression pattern, although the frequency of CD3 and CD4 cells is not dramatically reduced. These allografts show a decreased frequency of interferon-gamma and interleukin (IL)-2-expressing cells and a slightly increased frequency of cells expressing IL-4 and IL-10, compared with unmodified acute rejection. A direct role of these changes in T-cell cytokine expression is demonstrated by reversal of tolerance induction and rejection of the allograft by in vivo injection of either anti-IL-10 or anti-IL-4 mAb.

CONCLUSIONS

Although there are significant differences in the frequency of different cellular subsets and patterns of cytokine gene expression, these differences are quantitatively subtle, suggesting a delicately balanced immune response that can develop a pattern of specific unresponsiveness, with relatively minor alterations in the specific T-cell response.