Development Of Cytotoxic Activity Research Articles

CD80, CD86 and CD40 provide accessory signals in a multiple-step T-cell activation model.

In this review, a sequential multiple-step model for T-cell activation is proposed. In a series of in vitro studies, highly purified freshly isolated human peripheral blood T lymphocytes were stimulated through the CD28 receptor, with mAb or with natural ligands B7-1 or B7-2, along with TCR stimulation, in the absence of other costimulatory interactions. Ligation of the CD28 receptor, along with stimulation of the TCR, was found to up-regulate pleiotropic in vitro activities, including the secretion of both Th1 and Th2-type cytokines, B-cell help, and the development of cytotoxic activity. This costimulatory action involves CD4+ and CD8+ as well as naive and memory T-cell subsets. The expression of B7-1 and B7-2 on professional APC in situ in both normal and pathological tissues, and its up-regulation on monocytes by GM-CSF and IFN-gamma is consistent with this role. Additional studies have addressed the contribution of interactions between CD28 and B7-1 and B7-2 in T-cell activation initiated by normal un-engineered APC, such as stimulation with recall antigens and primary MLR. Blockade of the interaction between CD28 and B7-1/B7-2 under these conditions failed to completely inhibit T-cell responses or to induce anergy. Complete inhibition and anergy were, however, induced with a combination of CsA, targeting downstream TCR-triggered signalling, as well as anti-B7-1- and anti-B7-2-directed reagents. Interestingly, and in contrast to anti-LFA-1 mAb, the addition of anti-B7-1 or anti-B7-2 reagents could be delayed until at least 48 h after the initiation of T-cell stimulation, indicating a requirement for a late interaction between CD28 and its counter-receptors. Interactions between CD40L on activated T cells and CD40 on APC may serve to sustain, enhance or prolong the presentation of B7-1 or B7-2 on the APC, and thus to prevent anergy induction, or ineffective or abortive T-cell stimulation. Based on these data a sequential multiple-step T-cell activation model is proposed, and novel strategies for immuno-intervention can be designed.

Antioxidant treatment of diabetic rats inhibits lipoprotein oxidation and cytotoxicity.

Increased lipid peroxidation products were detected in a lipoprotein fraction containing very low density lipoprotein (VLDL) and low density lipoprotein (LDL) obtained from rats made diabetic by streptozotocin injection. The enhanced oxidation in the diabetic VLDL plus LDL fraction correlated with the in vitro toxicity of this lipoprotein fraction to proliferating fibroblasts. In contrast, high density lipoprotein (HDL) was not cytotoxic. That the increased oxidation and development of cytotoxic activity in the diabetic VLDL + LDL was related to the diabetes was shown by the fact that insulin treatment of diabetic animals inhibited both oxidation and cytotoxicity of VLDL + LDL. In contrast, treatment of diabetic rats with the antioxidants vitamin E or probucol after diabetes was established also inhibited both the in vivo oxidation and in vitro cytotoxicity of diabetic VLDL + LDL, but without altering hyperglycemia. Vitamin E or probucol treatment thus allowed separation of the oxidation process from the hyperglycemia occurring in experimental diabetes. The mechanisms by which diabetes in humans or experimental animals leads to the various manifestations of tissue damage are unknown; however, these studies demonstrate for the first time that a relationship exists between the in vivo oxidation of lipoproteins in diabetes and the potential for tissue damage as monitored by in vitro cytotoxicity. Furthermore, these results suggest that the mechanism for certain aspects of tissue damage accompanying experimental diabetes may be mediated by lipid peroxidation products.

Induction of lymphokine-activated killer cells against human leukemia cells in vitro

The induction of lymphokine-activated killer (LAK) cells against fresh human leukemia cells was investigated. Two thirds of the 62 leukemias examined were susceptible to the lytic effect of allogeneic IL-2 induced LAK cells in vitro. No substantial differences could be detected between myeloid or lymphoid leukemias or with regard to the FAB subtype or the immunophenotype. Culturing mononuclear cells from peripheral blood or bone marrow of leukemia patients with IL-2 resulted in an expansion of residual large granular lymphocytes and development of cytotoxic activity. The combination of IL-2 with IFN-gamma or the presence of tumor cells during the activation process led to an enhancement of LAK cell cytotoxicity. These results suggest that LAK cells may be useful in the treatment of leukemia.