Restoration of allograft responsiveness in B rats. IV. The divergent migratory behavior of lymphocyte populations mediating cardiac allograft rejection

Physical characterization of cyclosporine binding sites in lymphocytes

The binding of cyclosporine to human peripheral blood lymphocytes (PBLs) was studied by measuring the fluorescence emission spectrum and lifetime of the fluorescent and immunosuppressive cyclosporine derivative dansyl-cyclosporine (DCs). The emission maximum and fluorescence lifetime of DCs were characterized in several solvents. The fluorescence emission maximum and lifetime of DCs increased at a high dielectric constant. The fluorescence lifetime decay curve of DCs was a monoexponential function in all solvents tested. Fluorescence micrographs of lipid vesicles and erythrocytes labeled with DCs exhibit uniform staining patterns, whereas PBLs show heterogeneous DCs labeling. DCs exhibits a relatively low emission maximum (490 nm) in erythrocyte membranes. Such an emission maximum is characteristic of a hydrophobic environment. DCs in PBLs also has a low emission maximum (484 nm). The lifetime of DCs in PBLs required two exponential terms to properly fit the lifetime decay curve and could not be attributed to light scattering. One short component (4.7 +/- 1.0 ns) and a second long component (18.5 +/- 1.0 ns) were resolved from the DCs fluorescence decay curves. Time-resolved anisotropy of DCs in PBLs revealed that the labeled drug was present in an anisotropic environment, consistent with at least some DCs being bound to a membrane. These fluorescence studies suggest that DCs interacts with multiple and/or heterogeneous sites in peripheral blood lymphocytes.

Lymphocyte migration patterns in organ allograft recipients

A central tenet of immunology is the observation, made 30 years ago, that lymphocytes recirculate continuously between peripheral blood and lymphoid tissues. In recent years, the subject of lymphocyte migration, both under physiological conditions and in states of alloresponsiveness, has become more enigmatic. It lies outside most current topics of immunological investigations, labelling and tracing techniques are problematic, and many experimental findings are phenomenological and difficult to interpret. Indeed, our overall knowledge of the functional differences between the various host lymphoid compartments and their constituent cell populations remains rudimentary. However, as understanding increases regarding the host immunological events responding to an antigenic stimulus such as a graft, with growing definition of the distinctive and interconnecting roles of lymphocyte subpopulations and their products acting on each other to produce graft destruction, the conceptual importance of lymphocyte migration again is becoming obvious. This role includes many facets of immunity such as the effects of antigen specificity, immunologic memory, differential behavior of recirculating or sessile populations, and local and systemic contact between antigen and effector cells. It has become evident that lymphocytes migrate in a non-random and highly dynamic fashion determined by a range of specific and non-specific factors; in the setting of organ transplantation, patterns are profoundly affected by the interrelated cellular and humoral components of the immunological cascade which may lead either to graft rejection or to its prolongation in untreated and immunologically modified recipients, respectively. Thus, the traffic of lymphocytes throughout host lymphoid and non-lymphoid compartments and their activity within these compartments should be considered an integral part of the host immunomodulation triggered by transplantation of histoincompatible tissue. Gradual filling of the gaps in our current knowledge on the mechanistic aspects of this phenomenon will not only contribute to basic science itself, but also should lead to the development of innovative therapeutic approaches to treat graft rejection.

Therapy with monoclonal antibody to interleukin 2 receptor spares suppressor T cells and prevents or reverses acute allograft rejection in rats

The mouse hybridoma ART 18 monoclonal antibody (mAb), which binds to the rat interleukin 2 (IL-2) receptor, was studied for its effect on heterotopic cardiac allograft survival in two histoincompatible inbred rat strain combinations. Treatment with ART 18 mAb for 10 days after transplantation prolonged allograft survival in a dose-dependent fashion up to about 3 weeks (acute rejection normally occurs within 8 days). ART 18 mAb therapy started at 5 days after transplantation the time of major rejection activity) abrogated acute rejection and extended the survival to about 18 days. The dense cellular infiltrate noted histologically in acute rejection had virtually disappeared after ART 18 mAb treatment. Thus, IL-2 receptor-targeted therapy can be successfully used to prevent and/or treat acute rejection. When spleen cells from antibody-treated recipients bearing well-functioning allografts were adoptively transferred to normal untreated rats that received cardiac allografts 24 hr later, the survival of donor-specific, but not third-party, test cardiac allografts was prolonged significantly; this supports the idea that ART 18 mAb induced "sparing" of suppressor T lymphocytes. Combining infusion of ART 18 mAb with exogenous IL-2-rich conditioned medium produced the same effect as if the mAb alone had been administered, suggesting that an excess of IL-2 does not prevent binding of ART 18 mAb to IL-2 receptor-bearing cells in vivo. These results support the important role of the IL-2 receptor-bearing cells in the mechanism of allograft rejection; they may represent an important target for immunosuppression in clinical organ transplantation.

Behavior of helper T lymphocytes in cyclosporine-mediated long-term graft acceptance in the rat

(LEW X BN)F1 cardiac allografts are rejected acutely (7 days) in unmodified LEW rats, yet survive indefinitely following cyclosporine (CsA) treatment (15 mg/kg im for 7 days) or in T-cell-deprived (B) recipients. Using these models, the function of T helper cells (Th) in the maintenance phase of CsA-mediated long-term graft survival was examined. With monoclonal antibody immunoaffinity fractionation techniques, Th (W3/25+OX8-) were separated from spleens of CsA-treated hosts 3-4 weeks after grafting (CsA-Th), from specifically sensitized (s-Th), or from normal ungrafted (n-Th) rats. Adoptive transfer of 60 X 10(6) CsA-Th into B recipients produced rejection of donor-specific, but not third-party grafts in 21 +/- 7 days, comparable to s-Th (17 +/- 4 days), but faster than n-Th (4-5 weeks, P less than 0.025). CsA-Th recombined with T cytotoxic/suppressor phenotype (CsA-Tc/s, OX8+W3/25-) in numbers contained in 100 X 10(6) CsA-T cells were ineffectual, even when supplemented with exogenous interleukin 2-rich conditioned medium (IL-2CM); in contrast 100 X 10(6) s-T cells + IL-2CM inevitably caused acute rejection in B hosts (11 +/- 3 days). Increasing numbers of Th incrementally to 100 X 10(6) augmented the effectiveness of s-Th (rejection in 13 +/- 2 days), but did not improve potency of CsA-Th (20 +/- 2 days). Suppressor activity produced by small numbers of contaminating CsA-Tc/s (c. 0.4%, 4-5 X 10(5) cells in 100 X 10(6) CsA-Th) accounted for extended graft survival in B recipients, as this small number of CsA-Tc/s transferred into untreated syngeneic rats increased test graft survival to c. 16 days (P less than 0.001). IL-2 production by spleen cells, depressed during CsA treatment, returned to normal levels 2-3 weeks following drug withdrawal, whereas transfer of CsA-Th into B recipients induced a shift of IL-2 levels from dramatically depressed to normal, findings suggesting normal IL-2 production by CsA-Th. This report demonstrates that an unresponsive state in CsA-treated animals is achieved despite the presence of fully potent donor-specific Th. Active suppressor activity plays a critical role in the maintenance phase of graft survival in rats treated transiently with CsA.