Effects of cyclosporin A on the activity of mouse natural killer cells and hybrid resistance

Positive and negative regulation of Natural Killer cells: therapeutic implications

Natural Killer (NK) cells can mediate numerous anti-tumor and anti-viral effector functions as well as play important immunoregulatory roles in various disease states. Promoting the ability of NK cells to respond in an immunotherapeutic setting has often been sought by the addition of NK cell-stimulating factors. However, such therapies are often found to be insufficient, which may in part be due to the presence of inhibitory influences on the NK cell. NK cells can respond to a plethora of cytokines which are generated by numerous cell types and these interactions can markedly affect NK cell survival and activity. NK cells also possess multiple activating and inhibiting receptors which can alter their function. Whether the NK cell will become activated or not can depend on a complex balance of activating and inhibitory signals received by the cell and modulation of these signals may shift the balance on NK activation. This review discusses the various activating and inhibitory stimuli which can act on NK cells, and suggests that future NK cell-based therapies consider not only activating stimuli but also removal of possible inhibitory elements which could prevent optimal NK cell function and/or survival.

Regulation of liver regeneration by interleukin-2 and its inhibitors: cyclosporine A and FK 506

Several investigations have been suggesting that lymphocytes can be responsible for growth regulation of liver. The interleukin-2 (IL-2) production by spleen cells was noted to be increased 2 days after resection of 70% of the volume of the liver in C3H/He mice. The effects of IL-2 production and its antagonists: cyclosporine A (CsA) and FK506 on liver regeneration were thus studied by measuring in vivo incorporation of Bromodeoxyuridine (BrdU). By intraperitoneal injection of IL-2 5 times every 8 h after hepatectomy. BrdU labeling indices at 36 h after the operation were suppressed in a dose-dependent manner. On the other hand, treatment with CsA and FK506, which inhibit IL-2 production, increased the mitotic indices of the regenerating livers. Serum levels of aminotransferases were not affected by FK506 at a dose sufficient for the mitotic stimulation. Based on these results, CsA and FK506 would appear to stimulate liver cell proliferation by suppressing IL-2 production and inhibiting of NK cell activity.

Effects of cyclosporin on C57BL/6 splenocytes before and after culture with high-dose recombinant interleukin-2: implications for immunosuppression with cyclosporin

Lymphokine-activated killer cells appear to arise from precursor cells bearing natural killer (NK) cell antigens. Cyclosporin (CsA) is a well-known immunosuppressive agent that can down-regulate NK cell cytotoxicity. Studies were initiated to evaluate the effects of CsA on splenocytes before and after exposure to recombinant interleukin-2 (rIL-2). Normal C57BL/6 mice receiving CsA at a dose of 100 mg/kg demonstrated a decrease in NK cell lysis against the YAC-1 lymphoma target in a 4-h chromium-release assay. When splenocytes obtained from CsA-treated mice were cultured for 3 days in complete medium containing 1000 U rIL-2/ml, they demonstrated a return of NK cell lysis to normal (mean cytotoxicity = 65 LU versus 60 LU for control and CsA-exposed splenocytes respectively; P, NS, five consecutive experiments) but revealed a decrease in the lysis of a NK-resistant target: the MCA-102 sarcoma (mean cytotoxicity = 20 LU vs 12 LU for control and CsA-exposed splenocytes respectively; P less than 0.02, five consecutive experiments). Fresh splenocytes cultured in media containing rIL-2 and CsA demonstrated a decrease in proliferation, cell-cycle S-phase fraction and cell yields compared to splenocytes cultured in media containing rIL-2 alone. In addition, a decrease in tumor cell lysis for NK-cell sensitive (mean percentage lysis = 98% vs 60%, rIL-2 vs rIL-2 + CsA; effector-to-target ratio 100: 1) and resistant targets (mean percentage lysis = 68% vs 28%, rIL-2 vs rIL-2 + CsA; effector-to-target ratio 100: 1) was also seen. CsA had no effects on the phenotypic antigenic expression of splenocytes cultured with high-dose rIL-2 although activated T cell antigens were down-regulated when fresh splenocytes were evaluated after in vivo exposure to CsA. These studies support the down-regulating effects of CsA on NK cell lysis and suggest that the rIL-2-activated cell population is heterogeneous as demonstrated by the differential down-regulation and recovery of NK-resistant cell lysis versus NK-sensitive cell lysis.