Decreased natural killer-type activity of spleen cells against immature thymocytes in autoimmune strains of mice

Recently we have reported that normal natural killer (NK)-enriched murine spleen cells have the capacity to lyse immature thymocytes of syngeneic or allogeneic origin. The studies presented in this paper show a different pattern of NK-type cytolysis and thymocyte sensitivity in mice which later in life develop autoimmune disease. Such mice appeared to have reduced effector NK capacity and thymocytes from these mice seemed to have reduced sensitivity as targets. This may allow presence and persistence of autoreactive T cell subpopulations which would normally be eliminated.     

Enhanced natural killer (NK) cell activity and NK-sensitive thymic cells in murine muscular dystrophy

Studies have shown that there is an abnormality in the thymus of dystrophic mice with respect to age-dependent thymus weight changes and altered morphology (T. DeKretser and B. Livett, Nature (London), 263, 682, 1976). Recently, others have shown that natural killer (NK) cells can lyse cells of a large, immature, rapidly dividing cell subpopulation within the thymus of normal young (3 weeks of age) mice (M. Hansson, K. Karre, R. Kiessling, J. Roder, B. Anderson, and P. Hayry, J. Immunol., 123, 765, 1979). The NK susceptibility of dystrophic mouse thymocytes as targets was therefore studied. Spleen cells from normal (+/+) and dystrophic ($\text{dy}{}^{\mathrm{2J}}\text{dy}{}^{\mathrm{2J}}$) male C57BL/6J mice 8–10 weeks old were passed over nylon wool and the nonadherent cells were incubated with ⁵¹Cr-labeled YAC-1 lymphoma target cells or thymocytes in a ⁵¹Cr-release assay. Spleen cells from dystrophic mice killed twofold more YAC-1 target cells than did spleen cells from normal mice. Thymocytes from 3- to 4-week-old dystrophic mice were three to four times more susceptible to NK lysis by dystrophic mouse spleen cells as compared with normal mouse spleen cells. Spleen cells from dystrophic mice had the same NK activity against dystrophic and normal mouse thymocytes as targets. Normal mouse spleen cells killed three- to fourfold more dystrophic mouse thymocytes than that of normal mouse thymocytes as targets. Target cellbinding studies revealed that conjugate-forming cells from nylon nonadherent dystrophic mouse spleen cells were found to be two- to fourfold greater than for normal mouse spleen cells using YAC-1 tumor cells as targets. The number of lymphocytes bound per YAC-1 target cell ranged from 2 to 5 for dystrophic mouse spleen cells as compared with 1 to 2 for the normal control group. Using both normal and dystrophic mouse thymocytes as targets, the conjugate-forming cells from dystrophic mouse spleen cells were also found to be twofold greater than in the normal control group. Cold target inhibition studies revealed that the natural killing of dystrophic mouse thymocytes was due to a YAC-1-reactive NK cell. Effector cell depletion studies using monoclonal anti-Thy-1.2 plus complement treatment and plastic petri dish adherence also revealed that the natural killing of dystrophic mouse thymocytes was not due to either T lymphocytes or macrophages. Taken together, these results show an increase in NK-sensitive thymocyte targets in dystrophic mice, in combination with an increase in splenic NK activity.     

Antiviral effect of lymphokine-activated killer cells: characterization of effector cells mediating prophylaxis

Lymphokine-activated killer (LAK) cells generated by cultivation of C57BL/6 mouse spleen cells in the presence of recombinant interleukin-2 were transferred into natural killer (NK) cell-deficient suckling mouse recipients. These mice were then challenged with either murine cytomegalovirus (MCMV) or lymphocytic choriomeningitis (LCMV) and sacrificed 3 days later. No interleukin 2 infusions were given. Mice receiving as few as 5 x 10(5) LAK cells had several 100-fold decreases in spleen MCMV titers as compared with untreated mice. This treatment had no effect on spleen LCMV titers. The LAK cell cultures contained 10 to 17% NK 1.1+, 50 to 55% Lyt-2+, and 33 to 50% immunoglobulin D+ cells. Double fluorescence labeling and in vitro cytotoxicity assays with fluorescence-activated cell sorting revealed at least two mutually exclusive killer cell populations. NK 1.1+ LAK cells resembled freshly isolated activated NK cells with regard to target cell range (YAC-1 cell killing greater than L-929, P815, and EL-4 cell killing), large granular lymphocyte (LGL) morphology, and decreased ability to lyse interferon (IFN)-treated target cells. Lyt-2+ LAK cells lysed the targets mentioned above but at lower levels and without the differences in susceptibility mentioned above. These Lyt-2+ LAK cells also had a decreased ability to lyse IFN-treated targets, in contrast to classic cytotoxic T lymphocytes, which lyse IFN-treated targets far more efficiently than untreated targets. Purified populations of LAK cells obtained by fluorescence-activated cell sorting were used in the antiviral protection model. The results showed that protection against MCMV could be mediated by NK 1.1+, NK 1.1-, Lyt-2+, Lyt-2-, and IgD- populations but not by IgD+ cells. The five protective populations all had in common the LGL phenotype and cytotoxic activity in vitro. The IgD+ population did not contain LGLs, lyse target cells in vitro, or mediate an antiviral effect in vivo. These results suggest that LAK cells may be therapeutically useful against certain virus infections (MCMV) but not others (LCMV) and that despite their heterogeneity in antigenic phenotype and cytotoxic activity, their pattern of antiviral activity in vivo resembles that of NK cells, which protect against MCMV but not LCMV.     

Natural cytotoxicity against mouse hepatitis virus-infected target cells. I. Correlation of cytotoxicity with virus binding to leukocytes

Spleen cells from uninfected control mice selectively lysed BALB/c 3T3 fibroblasts infected with mouse hepatitis virus (MHV), a murine coronavirus. Lysis of infected cells occurred within 3 hr, and histocompatibility between effector and target cells was not required. This natural, cell-mediated, virus-associated cytotoxicity differed from NK cell- and T cell-mediated lysis. Spleen cells from animals infected with MHV were enriched in NK activity and were more cytotoxic to YAC-1 target cells, but did not show enhanced cytotoxicity for MHV-infected target cells. Spleen cells from beige mice, which are deficient in NK cell activity, were able to lyse MHV-infected target cells, as were spleen cells from nude mice, which are deficient in T cell activity. Lysis of MHV-infected target cells could be mediated by cells from the spleen and, to a lesser extent, by cells from the bone marrow, but not by resident peritoneal cells or thymocytes. We suggest the term "virus killer (VK) activity" for this phenomenon. VK activity of splenocytes from different mouse strains correlated with the ability of the splenocytes to bind purified radiolabeled MHV virions. MHV virions caused agglutination of spleen leukocytes from susceptible mouse strains, indicating that leukocyte agglutination or adsorption may provide a useful assay for coronaviruses such as MHV which lack hemagglutinating activity. SJL mouse splenocytes did not bind MHV and did not lyse infected targets. MHV bound relatively well to splenocytes of other mouse strains, but poorly to thymocytes and erythrocytes. Binding of MHV to leukocytes was not influenced by 6 mM EDTA or EGTA, indicating a lack of requirement for Mg++ or Ca++. VK activity was also resistant to EDTA and EGTA, in contrast to NK activity, which was sensitive to those chelating agents. VK activity was also unaffected by actinomycin D, cycloheximide, or puromycin, indicating that new protein synthesis was not required for lysis. Antibody to interferon-alpha/beta did not block lysis, nor was there substantially enhanced lysis mediated by leukocytes from mice infected with virus and thus exposed to high levels of interferon. VK activity was blocked by antibody directed against the peplomeric glycoprotein E2 of MHV. VK activity required infected target cells, because cells with adsorbed MHV virions were not lysed by splenocytes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Induction of natural killer cell activity and perforin and granzyme B gene expression following continuous culture of short pulse with interleukin-12 in young and old mice

Anticancer immunotherapy with cytokines is often limited by the occurrence of severe toxicity, particularly in older age groups, which are characterized by a reduced tolerance to antineoplastic therapies. We, and others, have recently demonstrated the efficacy of pulsing procedures with IL-2 as a new therapeutic strategy to induce antitumor cytotoxic cells. The aim of this paper was to evaluate the effect of IL-12 on NK cell activity in young and old mice and to investigate the possibility of inducing NK cytotoxicity and perforin and granzyme B gene expression through a brief exposure of spleen lymphocytes from young and old mice to IL-12. Pulsed lymphocytes were compared with non-pulsed cells cultured continuously in IL-12. IL-12 was able to boost both endogenous and IL-2-induced NK cell activity in young and old mice; the levels of cytotoxicity were lower in old than in young animals although the relative increase of IL-12 plus IL-2 versus IL-2 alone was greater for old mice. Comparable levels of NK cell activity were obtained in pulsed (5 min-1 hour) and non-pulsed lymphocytes from both young and old mice after one or three days of culture. The efficacy of the pulsing procedure was evident in both endogenous and IL-2-induced NK cytotoxicity. The mRNA encoding perforin and granzyme B were markedly and similarly enhanced in both IL-12-pulsed and non-pulsed lymphocytes in comparison with control cells. The results demonstrate the effectiveness of IL-12 pulsing in inducing antitumor cytotoxic cells, suggesting the possibility of using IL-12 pulsing, alone or in combination with IL-2, in the immunotherapy of both young and old subjects.     

Influence of dietary restriction and aging on natural killer cell activity in mice

Natural killer cells (NK) are believed to defend against tumor growth. Because rodents subjected to dietary restriction without malnutrition live longer and develop spontaneous tumors less often or later in life than unrestricted controls, we measured NK activity in restricted and in unrestricted mice. An age-related decline in NK responses to YAC-1 tumor target cells was detected in both groups. NK responses for control mice were highest in 2- to 3-mo-old mice, sharply reduced in middle-age mice (14 to 15 mo), and slightly reduced further in old mice (30 to 33 mo). At all ages the response of restricted mice was less than that of controls. However, after injection with Poly I:C (which increases NK activity), old restricted mice showed NK cytolysis not different from young mice on either diet, and substantially higher responses than old unrestricted mice. In addition, restricted mice showed increased in vitro generation of cytotoxic T lymphocytes (CTL) to YAC-1 and P815 compared with age-matched controls. Restricted mice may better resist cancer via an NK system very responsive to induction signals coupled with a CTL system more effective than that of unrestricted controls.     

Elevated natural killer cell-mediated cytotoxicity, plasma interferon, and tumor cell rejection in mice persistently infected with lymphocytic choriomeningitis virus

To assess the effects of chronic virus infection on NK cells, the related phenomena of interferon (IFN) production, NK cell activation, and resistance to tumor implants were studied in mice persistently infected with lymphocytic choriomeningitis virus (LCMV). NK cells from these LCMV-carrier mice displayed augmented killing of the NK-sensitive YAC-1 target cell. They did not lyse the more resistant targets L-929 and P815, whereas NK cells from acutely infected mice efficiently lysed all three cell types. The plasma from LCMV-carrier mice contained an antiviral substance identified as IFN type I, based on species specificity, virus nonspecificity, resistance to pH 2, and sensitivity to antibody to type I IFN. IFN titers in plasma from LCMV-carrier mice were 32 to 64 U/ml, about 20-fold less than those in acutely infected mice. Both the IFN and NK cell levels continuously remained elevated in the LCMV carrier mice up to at least 6 months of age. IFN is known to activate NK cells and to induce their blastogenesis in vivo. As determined by centrifugal elutriation, large NK blast-size cells were isolated from the spleens of acutely infected mice, but not from either normal or LCMV-carrier mice, suggesting augmented NK cell-mediated lysis in the absence of enhanced proliferation. Poly inosinic-cytidylic acid induced high levels of NK cell-mediated cytotoxicity and blastogenesis in both control and LCMV-carrier mice, but IFN was induced to lower levels in carriers as compared with controls. Coincidental with augmented NK cell activity, the LCMV-carrier mice rejected intravenously injected 125IUdR-labeled tumor cells more efficiently than did normal mice. Thus, LCMV carrier mice have low levels of type I IFN, moderately augmented NK cell activity lasting for at least 6 months, and increased resistance to tumor cell implants. This indicates that augmented NK cell-mediated cytotoxicity can be maintained in vivo over prolonged periods of time in the presence of chronic low-level IFN stimulation.     

Natural killer cell activity in murine muscular dystrophy. III. NK-sensitive myoblast cells and lack of NK activity in beige/dystrophic hybrid mice

The NK-susceptibility of dystrophic mouse myoblast cells was investigated. Spleen cells from 8- to 10-week-old normal (+/+) and dystrophic (dy2J/dy2J) male C57BL/6J mice were fractionated on Percoll density gradients and the cells at each density interface were incubated with either 51Cr-labeled YAC-1 or myoblast cells in a 6 hr 51Cr-release assay. Myoblast target cells were obtained from either heterozygous (+/dy2J) or homozygous (dy2J/dy2J) muscle cultures or a transformed tetraploid myoblast line (M14D2). The data indicate that the interface between the 50 and 60% (1.060-1.075 g/ml) Percoll density fractions of spleen cells from either normal or dystrophic mice contains the largest proportion of asialo GM-1 positive and NK-1 positive cells displaying NK activity. Myoblast cells from either heterozygous (phenotypically normal) or homozygous dystrophic mice were not significantly different in susceptibility to NK-mediated lysis by Percoll enriched normal or dystrophic mouse NK cells. However, dystrophic mouse spleen cells had the highest NK activity against both myoblast targets as compared with normal mouse spleen cells. The transformed myoblast cell line, M14D2, was significantly less susceptible to NK-mediated lysis by dystrophic mouse spleen cells when compared with freshly cultured myoblast target cells. Target cell binding studies revealed that conjugate forming cells from the 50% Percoll density interface of dystrophic mouse spleen cells were approximately twofold greater than that of normal mouse spleen cells against either heterozygous or homozygous dystrophic mouse myoblast targets. Cold target inhibition studies revealed that the natural killing of dystrophic mouse myoblast cells was due to a YAC-1 reactive NK cell. Breeding experiments between C57BL/6J homozygous "beige" (bgJ/bgJ) mutant mice and dystrophic (dy2J/dy2J) mice produced beige/dystrophic hybrid mice which displayed clinical symptoms of the dystrophy process by 3 to 4 weeks of age. Spleen cells from these hybrid mice showed no significant differences in NK activity against YAC-1 target cells when compared with homozygous beige mice. Taken together, these results demonstrate the first reported evidence that murine myoblasts are susceptible to NK-mediated lysis. In addition, the data indicate that although dystrophic mouse NK cells recognize myoblast cells as targets, the NK cell studies with the beige/dystrophic hybrid mice do not indicate a direct in vivo role for NK cells in the dystrophy process.     

Effects of the peptide toxin from Microcystis aeruginosa on intracellular calcium,pH and membrane integrity in mammalian cells

Extracts of water blooms of the toxic cyanobacterium Microcystis aeruginosa showed a range of toxicities not related to their ability to lyse mammalian red cells. The HPLC-purified heptapeptide toxin (mol. wt. 1035) from Microcystis did not lyse red cells at up to 500-fold higher concentrations than that required to kill mice. This toxin (LD₅₀ 110 μg/kg for male mice) was used to investigate in vitro effects on isolated thymocytes, hepatocytes, mammary alveolar cells, and cultured Swiss 3T3 fibroblasts. Thymocytes were stimulated to progressive Ca²⁺ entry by toxin (0.1–10 μg/ml), reaching a peak after approx. 5 min. No deformation, intracellular pH change, Trypan Blue entry or cell lysis was seen within 60 min at 37°C. Hepatocytes were grossly deformed by the toxin, with a dose/response relationship between 0.1 and 1.0 μg/ml. No progressive Ca²⁺ entry was observed on toxin addition, instead a rapid rise in intracellular Ca²⁺, presumably from intracellular sources. No change in intracellular pH, Trypan Blue exclusion or cell lysis was observed over 60 min. Mammary alveolar cells and 3T3 fibroblasts were unresponsive to toxin at the concentrations tested. No change in protein synthesis or nucleic acid synthesis in thymocytes was observed after culture with 0.5 or 5.0 μg/ml toxin. It was concluded that cytoskeletal changes in deformed hepatocytes (the target cells in vivo) demonstrated the most probable cellular basis for toxicity, rather than changes in membrane permeability or cell metabolism.     

Renewal of natural killer cells in mice having elevated natural killer cell activity

The present study was designed to examined the dynamics of splenic natural killer (NK) cells under two conditions of enhanced NK cell activity: (1) CBA/J mice given polyinosinic-polycytidylic acid (poly-I:C), an NK-cell-enhancing agent, and 62) untreated athymic nude (nu/nu) mice. The 'total NK cell activity' of the spleen (percentage specific lysis corrected for changes in organ cellularity) increased 5-fold and 2.7-fold after poly-I:C treatment for 1 day and 4 days, respectively. An injection of hydroxyurea (HU), a cell-cycle-toxic drug, given together with either poly-I:C or saline to CBA/J mice resulted in both cases in a 25% reduction in total NK cell activity 1 day later. This suggests that the renewal rate of nondividing NK cells is similar in poly-I:C-treated and saline-injected mice, and that the NK-enhancing effect of poly-I:C is not due to a stimulation of proliferation among NK cell precursors. HU administered simultaneously with poly-I:C or saline for 4 days eliminated NK cell activity in both cases, indicating that spleen NK cell activity is mediated almost entirely by newly formed (less than or equal to 4 days) cells. In nude mice, NK cell activity was assayed at various intervals after an HU depletion period of 2 days. NK depletion was initially more rapid in nu/nu mice than in control (nu/+) mice, although equally profound, and the subsequent recovery of NK cell activity after cessation of HU was also more rapid than in control (nu/+) mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

Natural killer cells in the thymus. Studies in mice with severe combined immune deficiency

The relationship between NK cell and T cell progenitors was investigated by using mice with severe combined immune deficiency (scid). Scid mice are devoid of mature T and B cells because they cannot rearrange their Ig and TCR genes. However, they have normal splenic NK cells. Thymus of scid mice, although markedly hypocellular, contains cells that lyse YAC-1, an NK-sensitive tumor cell. By flow cytometry, two populations of cells were identified in the scid thymus. Eighty percent of the cells were Thy-1+, IL-2R(7D4)+, J11d+, CD3-, CD4-, CD8- whereas the remaining were IL-2R-, J11d-, CD3-, CD4-, and CD8-. By cell sorting, all NK activity was found in the latter population, which is phenotypically similar to splenic NK cells. To determine if the thymus contains a bipotential NK/T progenitor cell, J11d+, IL-2R+ cells were cultured and analyzed for the generation of NK cells in vitro. These cells were used because they resemble 15-day fetal and adult CD4- CD8- thymocytes that are capable of giving rise to mature T cells. Cultured J11d+ thymocytes acquired non-MHC-restricted cytotoxicity, but in contrast to mature NK cells, the resulting cells contained mRNA for the gamma, delta, and epsilon-chains of CD3. This suggests that J11d+ cells are early T cells that can acquire the ability to kill in a non-MHC-restricted manner, but which do not give rise to NK cells in vitro. The differentiative potential of scid thymocytes was also tested in vivo. Unlike bone marrow cells, scid thymocytes containing 80% J11d+ cells failed to give rise to NK cells when transferred into irradiated recipients. Together these results suggest that mature NK cells reside in the thymus of scid mice but are not derived from a common NK/T progenitor.     

Studies on the mechanism of low natural killer cell activity in infant and aged mice

NK activity in mice is high between about 6 and 10 weeks of age. In contrast, infant mice and mice older than 12-14 weeks of age usually have quite low or undetectable NK activity. Studies were performed to analyze the mechanisms underlying this characteristic age-related regulation of NK activity. Spleen cells from infant mice did not develop appreciable NK activity upon incubation for 12-18 h with either interferon (IFN) or interleukin-2 (IL-2). Analysis of the frequency of IL-2-dependent progenitors of NK cells, in a limiting dilution assay, also indicated that the spleens of infant mice are deficient in precursors of NK cells. In contrast, spleen cells from old mice (30 weeks old) developed substantial levels of NK activity upon incubation with either IFN or IL-2, and they showed a frequency of IL-2-dependent progenitors of effector cells that was similar to that of young mice. Both infant and old mice had plastic-adherent suppressor cells in their spleens, which could strongly inhibit NK activity. In addition, both infant and old mouse spleen cells contained nonadherent suppressor cells, which had a higher density on Percoll gradients than NK cells. Thus, several factors appear to contribute to the age-related regulation of NK activity in mice.     

Alpha-interferon induces remission in hairy cell leukemia without enhancement of natural killing

The number of large granular lymphocytes (LGL) and the capacity of peripheral blood mononuclear cells (PBMC) to lyse K 562 target cells in a natural killer (NK)-like fashion was evaluated in seven hairy cell leukemia (HCL) patients undergoing treatment with recombinant interferon-alpha-2 (rIFN-alpha-2). In HCL patients, whose peripheral blood showed high numbers (greater than or equal to 15 X 10(3)/microliters) of leukemic cells the number of LGL and their capacity to lyse K 562 tumor target cells were very low prior to treatment but increased significantly (p less than 0.05) following interferon (IFN) therapy. In patients with low numbers of hairy cells (HC) in their peripheral blood, both these parameters were higher and remained largely unaffected throughout IFN treatment. In vitro, HC proved to be completely insensitive to natural killing when tested against unstimulated and IFN-activated LGL from healthy donors. These results fail to support the concept of IFN-mediated enhancement of host antitumor actions, responsible for the favourable clinical results in HCL.     

Growth of tumor cells with different sensitivities for murine natural killer cells in young and adult athymic nude mice

Of four tumor cell lines, the murine YAC lymphoma, the human K562 lymphoma, and the human prostatic carcinomas PC3 and PC93, the susceptibility to murine natural killer (NK) cells as well as the tumorigenicity in young (3.5-4 weeks old) and in adult (8-10 weeks old) nude mice were studied. In young nude mice, which exhibited a lower level of NK cell activity than adult nude mice, the formation of solid tumors after inoculation of tumor cell suspensions occurred more frequently and with a shorter time lag than in adult animals. These effects were observed not only with the NK-sensitive YAC cells, but also with the relatively NK-insensitive PC3 and PC93 cells, indicating that also factors other than NK cell susceptibility may influence the growth of tumor cells in nude mice. Therefore, the use of young nude mice may enhance the rate of success of heterotransplantation of human tumors, regardless of the NK cell susceptibility of the tumor cells.     

Further characterization of natural killer cells induced by Kunjin virus

The natural killer (NK) cell induced one to two days after Kunjin virus infection of BALB/c mice is cytotoxic for a wide range of syngeneic, allogeneic and xenogeneic cell lines. It is also weakly cytotoxic for some non-malignant cells including mouse fibroblasts, macrophages and thymocytes, but not lymph node cells. Levels of lysis of non-tumour target cells are dependent on their genotype. Furthermore, malignant cell lines may become resistant following transplantation in vivo then susceptible again after culture in vitro. The virus-induced NK cell is elicited as readily in athymic (nude) as in normal mice. X-irradiation inhibits its development if administered prior to infection. It is labile on culture at 37 degrees. The cell carries Fc receptors but its NK activity is not antibody-dependent.     

Natural killer cell immunodeficiency in patients with chronic myelogenous leukemia. IV. Interleukin-1 deficiency, gamma-interferon deficiency and the restorative effects of short-term culture in the presence of interleukin-2 on natural killer cytotoxicity, natural killer-target binding and production of natural killer cytotoxic factor

We report herein that defective natural killer (NK) cell cytotoxicity, NK cytotoxic factor (NKCF) production and NK target binding ability of patients with chronic myelogenous leukemia (CML) are functionally restorable after short-term culture (less than 1 week) with recombinant interleukin-2 (rIL-2). We have previously reported that, despite normal to increased numbers of CD16+ large granular lymphocytes, fluorescence-activated-cell-sorted NK cells from CML patients are profoundly defective in NK cell activity and are unable to lyse the CML blast-crisis-derived, NK-sensitive target K562. Since we and others have also previously shown that the defective NK cytotoxicity from CML patients is restorable after 1-4 weeks of incubation with rIL-2, we therefore deemed it important to study the kinetics of IL-2-mediated NK restoration at earlier time intervals (less than 1 week). In the present report, we have demonstrated a significant restoration of NK cell cytotoxicity in CML patients against K562 after 5 days of short-term culture with rIL-2. In addition, recovery of NKCF production and restoration of target-binding capacity to normal levels by NK cells from CML patients were also observed after short-term (less than 1 week) rIL-2 treatment. Finally, we have demonstrated in the present report that adherent cells and peripheral-blood lymphoid cells from CML patients, as compared to normal controls, are unable to produce IL-1 beta and interferon-gamma, respectively, after stimulation with phorbol myristate acetate (IL-1 beta) and phytohemagglutinin-M (interferon-gamma).     

Lysis of human T cell leukemia virus infected T and B lymphoid cells by interleukin 2-activated killer cells

The human T cell leukemia (HTLV-1) retrovirus is the etiologic agent for adult T cell leukemia. Interleukin 2 (IL-2) activated killer (AK) cells have been shown to lyse freshly explanted tumor cells in vitro and have been used as a form of adoptive immunotherapy for the treatment of cancer. In this report, the ability of AK cells to lyse HTLV-1-infected targets was examined. Normal lymphocytes, when cultured in recombinant IL-2 for periods of 3 to 7 days, killed infected T and B cell lines. The precursor for these AK cells resided in the CD-16 antigen-positive subset (i.e., natural killer (NK) cells). Resting T cells, NK cells, or unfractionated lymphocytes did not lyse the infected targets. However, when isolated NK cells were incubated for 24 hr in IL-2, suboptimal cytolysis was induced whereas activation of NK cells with a four pulse of IL-2 was insufficient to generate effector cells. The results of performing cold target inhibition studies with Epstein-Barr virus-infected B cell lines and HTLV-1-infected T and B cell lines suggest that there are discrete subsets (i.e., clonotypic) in the AK population that preferentially lyse a given virally infected cell line. Thus to consider AK cells as true polyspecific killer cells may be inaccurate. Alternately AK cells may express a number of different receptors with variable affinities for the Epstein-Barr virus- and HTLV-1-infected cell lines. In addition, it was shown that HTLV-1-infected B cells are relatively resistant to AK cell-mediated lysis. These results clearly indicate that AK cells but not resting NK cells kill HTLV-1-infected cells.     

IFN increases class I MHC antigen expression on adenovirus-infected human cells without inducing resistance to natural killer cell killing.

It has been previously shown that unstimulated NK cells cannot preferentially lyse adenovirus serotypes 2 and 5-infected human cells. In this study, the ability of IFN to promote the selective NK cell-mediated lysis of adenovirus-infected human cells was determined. The relationship between target cell susceptibility to NK cell-mediated killing and class I Ag expression was also analyzed through the use of adenovirus serotype 2 and 5 mutants that do not make the adenovirus early region 3 19-kDa class I binding protein. IFN induced the selective lysis of adenovirus serotype 2 and 5-infected human cells by activating NK cells (IFN-alpha) and protecting uninfected, but not adenovirus-infected cells, from NK cell-mediated lysis (IFN-gamma). IFN-gamma increased the expression of class I Ag on the surface of cells infected with the adenovirus early region 3 deletion mutants, dl327 or dl801, to a level equal to or greater than that expressed on uninfected cells. Despite the increased expression of class I Ag, IFN-gamma could not protect these adenovirus-infected cells from NK cell-mediated lysis. Thus, dl327 or dl801 infection prevented IFN-gamma's induction of cytolytic resistance to NK cell-mediated killing but left IFN-gamma's induction of class I Ag intact. Surface class I Ag levels were substantially higher on IFN-gamma-treated, dl327-, and dl801-infected cells in comparison to cells infected with wild type adenovirus serotype 5. Again, higher target cell levels of class I Ag did not correlate with increased resistance to NK cell-mediated lysis because there was equivalent NK cell-mediated killing of IFN-gamma-treated adenovirus serotype 5-, dl327-, or dl801-infected cells. Thus, IFN-gamma only protects uninfected cells from NK cell-mediated killing, irrespective of target class I Ag levels, and thereby concentrates NK lytic activity on just adenovirus-infected cells. These data demonstrate that IFN-gamma's ability to protect target cells from NK cell-mediated cytolysis is unrelated to IFN-gamma's induction of surface class I MHC Ag.     

NK1.1+ thymocytes. Adult murine CD4-, CD8- thymocytes contain an NK1.1+, CD3+, CD5hi, CD44hi, TCR-V beta 8+ subset.

CD4-, CD8- thymocytes were purified from thymi obtained from normal C57BL/6 mice. By flow cytometry analysis, 5 to 10% of these double negative (DN) thymocytes were found to express NK1.1 on their surface. The NK1.1+ DN thymocytes were demonstrated, by two-color fluorescence, to be CD3lo, CD5hi, CD44hi, J11d-, B220-, MEL 14-, IL2R- with 60% expressing TCR-V beta 8 as determined by the mAb F23.1. In contrast, splenic and peripheral blood NK cells were NK1.1+, CD3-, CD5-, TCR-V beta 8- with 40 to 60% being MEL 14+. Unlike peripheral NK cells, fresh DN thymocytes enriched for NK1.1+ cells were unable to kill YAC-1, the classical murine NK cell target. However, these cells were able to mediate anti-CD3 redirected lysis even when they were assayed immediately after purification, i.e., with no culture or stimulation. These data demonstrate that adult murine thymocytes contain NK1.1+ cells which are distinct, both by function and phenotype, from peripheral NK cells. These data also raise the issue of a possible NK/T bipotential progenitor cell.     

Immunologic mechanisms in the pathogenesis of virus-induced leukemia. IV. Mechanism of target cell recognition by autoreactive thymocytes

Neonatal infection of mice with Moloney murine leukemia virus (MuLV-M) results in the establishment of a chronic virus-carrier state. Such MuLV-carrier mice exhibit several immunologic abnormalities including generalized immunosuppression and autoimmunity. Previously, we found thymocytes from MuLV-M-carrier mice to be cytotoxic for normal syngeneic and allogeneic fibroblasts but not for xenogeneic (hamster) target cells. However, when the same syngeneic or allogeneic target cells were infected with MuLV-M, they were "spared" from the autoreactivity, leading us to speculate that the MuLV receptor on the target cell membrane was involved in the autoreactivity. To address this question, we tested MuLV-carrier thymocytes for their ability to lyse hamster/mouse-hybrid target cells; some of which possessed chromosome 5 (which codes for the ecotropic MuLV receptor). Of the nine hybrid cell lines initially tested, only the five clones that carried chromosome 5 were killed by the autoreactive thymocytes. In additional experiments, we noted that the cytotoxic reaction was inhibited in the presence of a monoclonal antibody that reacts with an MuLV-M gp70 epitope. The results suggest that the autoreactive cytotoxicity is mediated, at least in part, through the formation of a "bridge" between MuLV budding from the membrane of the thymocytes and the ecotropic MuLV receptor on the target cells.