Mouse interferon preparations enhanced the specific cytotoxicity of sensitized lymphocytes for allogeneic target tumor cells. The factor responsible for the enhancement of cytotoxicity could not be dissociated from the antiviral activity of interferon by standard physicochemical means. Thus, in addition to its well-known antiviral activity, and its effect on cell division, interferon also appears to enhance a specialized cellular function. It is suggested that a common mechanism of action underlies these seemingly different biologic phenomena, and that interferon may play a role in the regulation of fundamental cellular processes.In addition to its well-known antiviral activity, interferon has been shown to inhibit the multiplication of tumor and normal'mammalian cells in culture (1-4). It seems likely, therefore, that the antiviral action of interferon is only one expression of the effect of interferon on cells (3, 4). In the course of our studies on interferon-cell interactions, we observed that prior treatment of sensitized splenic lymphocytes with interferon resulted in an enhancement of the specific cytotoxicity of these cells for target tumor cells. Thus, interferon appears to enhance a specialized cellular function. The results of these experiments and the evidence suggesting that interferon was the factor responsible for enhancement of cytotoxicity of sensitized lymphocytes for target tumor cells are presented herein. MATERIALS AND METHODSImmunization of Mice with L 1210 Cells. Mouse lymphoid leukemia L 1210 cells (5) were maintained by serial passage in ascitic form in DBA/2 mice. For immunization, C 57 BL/6 mice were injected intraperitoneally with 5 X 107 L 1210 cells. The spleens of immunized mice were usually harvested 10 days after injection.Lymphocytes. Suspensions of splenic lymphocytes from immunized or normal C 57 BL/6 mice were obtained according to the method of Brunner et al. (6). The washed lymphocytes were suspended in Eagle's medium containing 10% heatinactivated calf serum -at a density of 20 X 106 viable' cells per ml.Target Cells. L 1210 cells, an interferon resistant subline of L 1210 cells (7) (L 1210-R) and Ehrlich ascites cells (7) were grown in nonagitated suspension cultures in nutrient medium RPMI 1640 (Gibco), supplemented with 10% heatAbbreviation: NDV, Newcastle Disease Virus. 721 inactivated horse serum, 1% iL-glutamine (10 mM/ml), penicillin (200 U/ml), and streptomycin (40 pg/ml). For labeling with radioactive chromium (51Cr), 1 ml of a cell suspension (5 X 106 viable cells per ml) was incubated for 30 min at 37°with 0.1 ml of Na251CrO4 (200 uCi/ml, specific activity 400 mCi/mg of chromium, Centre d'Energie Atomique, France), according to the method of Brunner et al. (6,8). The cell suspensions were washed three times and readjusted to a density of 2 X 106 viable cells per ml.Interferon and Control Preparations. Mouse interferon preparations were obtained from the nutrient medium of monolayer cultures of MSV-Ia (9), L-929 (10), and L cells (11,12) that were inocula...

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Preparations of mouse interferon enhanced the expression of surface antigens of murine leukemia L 1210 cells, as determined by their alloantibodyabsorbing capacity. The factor responsible for the enhancement of surface antigen expression could not be dissociated from the antiviral activity of interferon by standard physicochemical means. Likewise, interferon did not increase the antibody-absorbing capacity of an interferonresistant subline of L 1210 cells. We conclude that interferon treatment of L 1210 cells is accompanied by modifications of the cell surface.In addition to the well-known antiviral action (1), interferon preparations also exert various biologic effects on cells (2-17). The nature of some of these effects suggested the possibility that interferon treatment might be associated with modifications of the cell surface. To test this hypothesis we have determined the effect of interferon on the surface antigen expression of mouse leukemia L 1210 cells by measuring their alloantibody-absorbing capacity. We report herein the results of these experiments. MATERIALS AND METHODSCell Culture. Murine leukemia L 1210 cells (18) and an interferon-resistant subline, L 1210-R (19), were cultivated in nonagitated suspension cultures in nutrient medium RPMI 1640 (Gibco), supplemented with 20% heat-inactivated horse serum and 1% i-glutamine (10 mmol/ml). EL4 cells (provided by Dr. K. T. Brunner) were cultivated in suspension cultures in the same nutrient medium, supplemented with 10% heat-inactivated calf serum, glutamine, asparagine (36 mg/liter) folic acid (6 mg/liter), and 5% trypticase soy broth.Interferon and Control Preparations. Preparations of mouse interferon were obtained from the nutrient medium of monolayer cultures of MSV-Ia (20), or C-243 cells (21) (provided through the courtesy of Dr. S. Baron) inoculated with Newcastle disease virus (NDV), and from brains of C57BI/6 mice inoculated intracerebrally with West Nile virus (22). Preparations of rabbit interferon were obtained from the nutrient medium of monolayer cultures of RK 13 cells, inoculated with NDV. Control preparations consisted of the medium of uninoculated cell cultures or tissues of uninoculated animals. Preparation and semipurification of murine interferon have been described (15 (L 1210 and EL4 cells were maintained by serial passage in ascitic form in DBA/2 and C57B1/6 mice, respectively). The mice were bled 1 week after the last injection. The sera were decomplemented and stored at -20°. Isoantisera prepared by intraperitoneal injection of C57B1/6 mice with Balb/c splenic lymphocytes or intraperitoneal injection of Balb/c mice with C57B1/6 splenic lymphocytes were generously provided by Dr. J. P. Levy.Labeling of Target Cells. For labeling with radioactive chromium (56Cr), 1 ml of a cell suspension (5 X 106 viable cells per ml) was incubated for 30 min at 370 with 0.1 ml of Na2CrO4 (2 mCi/ml, specific activity 400 Ci/mg of chromium, Centre d'Energie Atomique, France) (24).Cytotoxic Assay. 1 ml of 5"Cr-labeled target cells (2 X 1...

Treatment of young and mature mice with potent mouse, interferon preparations results in a marked enhancement of the expression of histocompatibility antigens on the surface of thymocytes and splenic lymphocytes as measured by an enhanced absorption of alloantiserum. We postulate that such modifications of the cell surface may reilect an effect of interferon on lymphocyte maturation and may be relevant to the effect of interferon on lymphocyte function.Since interferon can affect both the division and function of lymphocytes (1-17) it seems likely that it plays a role in the regulation of the humoral (6-11) and cell-mediated immune response (1,2,(12)(13)(14)(15)(16)(17). We have recently shown that incubation of mouse lymphoid cells with interferon was accompanied by a marked enhancement of the expression of surface histocompatibility antigens (18). The availability of potent semi-purified mouse interferon preparations (19) enabled us to determine whether treatment of mice with interferon would also result in modifications in the expression of histocompatibility antigens on thymocytes and splenic lymphocytes. (18) but may be summarized here as follows: spleen or thymus was homogenized gently in a Ten-Broek grinder with Eagle's minimal essential medium, and after sedimentation of large clumps of tissue the cell-rich supernatant was centrifuged. The cell sediment was washed once. Cell concentrations from control or interferontreated mice were adjusted so that the initial tube contained 20 X 106 splenic lymphocytes per ml or 40 X 106 thymocytes per ml. (Cell viability was determined by the trypan blue dye exclusion method. Cell mortality was always below 10%.) Tubes containing 2-fold dilutions of cells (in 1 ml) were centrifuged for 5 min at 800 X g in a refrigerated International Centrifuge. The supernatant was drained off and the cell sediment was incubated for 1 hr with an appropriate antiserum dilution corresponding to one cytotoxic unit, which is defined as % the dilution of antiserum which gave a 95% lytic end point in the cytotoxicity assay. The cells were again sedimented by centrifugation and 0.05 ml of the supernatant was harvested and assayed for remaining complement-dependent cytotoxicity for 5lCr-labeled L1210 target cells.To test the reliability (i.e., reproducibility) of this technique, a cell suspension was prepared from a pool of four spleens and several series of 2-fold dilutions were prepared from the same original cell suspension. Two such experiments comprised six series of 2-fold cell dilutions from a given cell suspension and a third experiment comprised eight series of 2-fold cell dilutions. It was found that the absorption curves (% specific 51Cr release from target cells after incubation with residual antiserum) were virtually superposable and the percent standard error at the 50% reduction point was 8%, 1%, and 15%, respectively.

The immune response of eight patients with mononucleosis caused by cytomegalovirus (CMV) was measured early in their illness--when virus was present in their urine and/or blood--and subsequently during convalescence. Levels of CMV-specific antibody rose early in the illness, but the proliferative response of mononuclear cells to CMV antigen did not reach the level characteristic of CMV-immune donors until several months later. The production of interferon by mononuclear cells in response to CMV antigen was also low early in the illness. Although these patients had prior immunity to herpes simplex virus and varicella-zoster virus, their mononuclear cells responded poorly to antigens prepared from these viruses. The proliferative response to these antigens returned to normal in parallel with the development of a normal response to CMV. It is suggested that acute CMV mononucleosis suppresses the proliferative response of human mononuclear cells.