Augmentation of cell-mediated cytotoxicity to a rat lymphoma. I. Stimulation of non-T-cell cytotoxicity in vivo by tumour cells

Biological activities of recombinant murine interferons alpha 1 and alpha 4: large difference in antiproliferative effect

The mature forms of two recombinant murine interferons alpha, alpha 1 and alpha 4, have been expressed in vitro using an established transcription and translation system. The relative specific antiviral activity, antiproliferative activity and the natural killer cell stimulating activity of both subtypes were compared in vitro. While the antiviral and natural killer cell stimulating activities of the 2 subtypes were similar, the relative antiproliferative activities varied markedly. On the basis of equal molar inputs, MuIFN-alpha 1 had less than 8% of the antiproliferative activity of MuIFN-alpha 4. This data shows that a large functional difference exists between these two subtypes which are known to be expressed at different levels in mouse L-cells in vitro.

Structure/function studies of murine interferon-alpha 1 using site-directed mutagenesis followed by in vitro synthesis

Site-directed in vitro mutagenesis followed by in vitro transcription and translation has been used to study structure/function relationships for murine interferon-alpha 1 (MuIFN-alpha 1). The mature form of the MuIFN-alpha 1 protein was expressed as well as analogue forms with amino acid substitutions at positions 33, 71, 72, 123 and 133. These positions were chosen on the basis of known human interferon-alpha structure/function relationships. Biological assays for antiviral activity on murine cells and natural killer cell activation have been performed for each of the proteins produced. The data obtained have been interpreted in the light of previous human and murine interferon-alpha structure/function work and the recently published three-dimensional structure of murine type I interferon.

In vivo boosting of lung natural killer and lymphokine-activated killer cell activity by interleukin-2: comparison of systemic, intrapleural and inhalation routes

Natural killer (NK) cells are thought to play a role in host defence against malignancy and infection, in immunoregulation and as precursor cells in a generation of lymphokine-activated killer (LAK) cells which can lyse NK-resistant tumour cells. As the lung is a major site for malignancy and infection and as there are large numbers of lymphoid cells including NK cells in the interstitial compartment of the lung, we evaluated the capacity of interleukin-2 (IL-2), a lymphokine capable of augmenting NK activity in vitro, to augment lung NK cell activity in vivo, using different routes of IL-2 administration. We compared both systemic (i.v. and i.p.) and local (intrapleural and inhalation) routes of IL-2 administration (50,000 U/daily for 5 days) using CBA mice, assessing NK and LAK cell activity in the spleen (systemic) and in the lung. The target cells used for these studies were the YAC-1 (NK-sensitive) and P815, NO36 and HA56 (NK-resistant, LAK-sensitive) cell lines. Splenic NK activity was increased by 1.4-1.9-fold for i.v./i.p., respectively, compared with controls with both systemic routes of administration, and lung NK activity was increased 3.2-fold and 3.8-fold (i.v./i.p, respectively, P less than 0.05), to levels which were comparable to systemic (splenic) NK activity following the same therapy. Intrapleural IL-2 administration similarly enhanced lung NK activity (3.3-fold) and splenic NK activity (1.3-fold; P less than 0.05 versus controls for both). Surprisingly, inhaled IL-2 suppressed both splenic and lung NK cell activity (84 +/- 8% and 78 +/- 10% suppression, respectively, P less than 0.05). LAK cell activity was also enhanced in the lung by 1.8-8-fold in response to i.v., i.p. and intrapleural IL-2, whereas inhaled IL-2 was ineffective in generating LAK cell activity. These results suggest that the systemic and intrapleural administration of IL-2 effectively boost pulmonary NK and LAK activity whereas inhalation of IL-2 does not. Thus, in clinical situations where boosting of local lung NK or LAK cell activity is desired, these routes of IL-2 administration may be effective.

The role of the thymus in the maintenance of natural killer cells in vivo

This report describes a model for investigating the role of the thymus in regulating natural killer (NK) cell activity in vivo. Evidence is presented that the thymus can regulate NK cells, and that at least some NK cells can develop without thymic help. Marrow from thymectomized rats depleted of circulating T cells by thoracic duct cannulation was transplanted into rats without a thymus (1 degree ATX.BM). These 1 degree ATX.BM rats had NK cell levels above controls 3 months after reconstitution but markedly depressed NK cell levels by 9 months. When 1 degree ATX.BM marrow was used to reconstitute rats with or without a thymus, those without a thymus (2 degrees ATX.BM) exhibited low NK cell levels after 3 months, and a similar result was obtained when 2 degrees ATX.BM marrow was used to reconstitute 3 degrees ATX.BM rats. The low NK cell levels in 2 degrees and 3 degrees ATX.BM rats were due to a deficiency in spontaneously cytotoxic NK cells, as they had normal numbers of interferon-responsive pre-NK cells. Spleen cells from 2 degrees and 3 degrees ATX.BM rats produced less interferon than control spleen cells when cultured with P815 tumor cells in vitro. However, 2 degrees and 3 degrees ATX.BM rats had higher numbers of large granular lymphocytes than controls despite their low NK cell levels. In marked contrast to 2 degrees and 3 degrees ATX.BM rats, spleen cells from 4 degrees ATX.BM rats had higher levels of cytotoxicity and a higher frequency of both spontaneously cytotoxic and pre-NK cells than controls. The 4 degrees ATX.BM rats also had the highest frequency of large granular lymphocytes in the spleen.

Interaction of African trypanosomes with the immune system

African trypanosomes cause disease in man and domestic animals. The parasites have the ability to escape immune control by two means: by antigenic variation of the surface glycoprotein coat so that waves of variant parasites arise and by inducing a general immunosuppression affecting immune responses to the parasite as well as to parasite-unrelated antigens. The cellular basis of the immune dysfunction will be discussed in relation to a mouse model system - it is the result of proliferative stimuli to T- or B-cells which then become refractory to selection by antigen and normal control signals. Recent experiments have focused on macrophages as important direct target cells for parasite action. We have obtained no evidence for a parasite derived mitogen acting directly on B- or T-cells. In vitro cell proliferation is associated with accessory cells and relates only to T-cells. During infection, macrophages become activated with changes in receptor expression and mediator release, so that there is, for example, spontaneous IL-1 release (with a role in T- and possibly in B-cell proliferation) and several-fold increases in PGE2 secretion, with its immunosuppressive activities. We also find parasitaemia-associated release of alpha-beta and gamma interferon by various cells which in turn influences immune function. The active parasite component is associated with parasite membranes, but its nature has not been further defined. We proposed that the macrophage changes provide a general pathway causing immune dysfunction associated with many infections, be they parasitic or caused by other invading organisms.

The mechanism of augmentation of natural killer cell activity by syngeneic tumor cells: role of macrophage-derived factor in NK boosting

The role of natural killer (NK) cells in controlling tumor growth was investigated using an NK-susceptible (c127v-IC2) and an NK-insusceptible (c127av) subline of the lymphoma L5178Y. Syngeneic DBA/2 mice inoculated intraperitoneally with c127v-IC2 tumor cells survived significantly longer than did c127av-bearing mice. Similarly, c127v-IC2, but not c127av tumor cells, were found to augment NK activity of spleen and peritoneal exudate cells in both DBA/2 and BALB/c nu/nu mice when inoculated into the peritoneal cavity. C127v-IC2 tumor cells incubated with either DBA/2 or BALB/c nu/nu spleen cells in vitro boosted NK activity and induced the production of gamma-type interferon (IFN), whereas incubation with c127av tumor cells induced neither NK activity nor IFN. Two kinds of cells cooperated in the production of IFN in response to c127v-IC2 tumor cells, namely, cells which were nonadherent, bore asialo-GM1, NK-1.2 and a low level of Thy-1.2 antigen and thus closely resembled NK cells, and those which were adherent and phagocytic and lacked both asialo-GM1 and NK-1.2 markers, presumably macrophages. Further analysis strongly suggested that c127-v-IC2 tumor cells stimulate macrophages to produce factor(s) which can induce the production of IFN by NK cells. The induced IFN was shown to be of the gamma type by its lability at pH 2.0 and insusceptibility to anti-IFN alpha, beta serum. This suggests a novel pathway for NK cell activation, and strongly supports the importance of macrophages and NK cells in natural resistance against certain tumors.

Evidence for a protective role of interferon in resistance to murine cytomegalovirus and its control by non-H-2-linked genes

Murine cytomegalovirus (MCMV) induces rapid production of a partially pH 2-stable type 1 interferon, the serum level of which is controlled by non-H-2-linked host genes. The production of high, intermediate, and low levels of interferon was found in C3H/He, C57BL/10, and BALB/c mice, respectively, and the use of H-2 congenic mice on the BALB/c or C57BL/10 background showed that H-2-associated genes were not involved. Administration of large (up to 200,000 U) daily doses of partially purified type 1 (alpha plus beta) interferon failed to protect low-producer BALB/c or BALB.K strains from lethal infection. Treatment of the higher (C3H/He) or intermediate (C57BL/10) producer strains with anti-type 1 interferon antibody significantly reduced their resistance to the virus; however, such treatment had no effect on the low-producer BALB/c strain. The decreased resistance of anti-interferon-treated C3H/He mice was accompanied by a transient reduction in serum interferon titers, decreased activation of natural killer cells, a markedly enhanced viremia, and increased viral titers in the liver. These data strongly support a protective role of interferon in defense against MCMV in certain strains of mice. Furthermore, these data suggest that previous observations of a correlation of non-H-2-linked, genetically determined resistance to MCMV with activation of natural killer cells may have its basis in the genetic control of interferon induction by MCMV.

Natural killer cell activity and response to phytohaemagglutinin compared with the histological diagnosis of patients with transitional cell carcinoma of the bladder

In vitro tests of immune reactivity in patients with transitional cell carcinoma (TCC) of the urinary bladder were compared with the clinical and histological diagnosis. Response of peripheral blood lymphocytes to the mitogen phytohaemagglutinin (PHA) tended to be reduced in patients with more advanced disease, although the difference between patients with advanced disease and those with early disease or controls was not statistically significant (P greater than 0.05). Assessment of natural killer (NK) cell activity in the same patients showed no change in levels of reactivity at any stage of the disease. There was no difference between the NK cell activity of patients with TCC of the bladder and normal controls.

Quantitative studies of natural immunity to solid tumours in rats. NK activity in animals with primary or transplanted spontaneous tumours

Natural killer (NK) cell activity was measured in a quantitative 6 h chromium release assay using sarcoma MC7 cells as targets. The total NK lytic activity present in the spleen and blood of tumour-bearing animals was compared with the corresponding values for age/sex/parity-matched animals. Rats with primary spontaneous tumours in the breast or subcutaneous sites showed normal levels of NK activity, while rats with primary spontaneous kidney tumours had elevated NK activity, the degree of augmentation being greater with increasing tumour size. A similar elevation of NK activity was generally found in animals with large, transplanted, spontaneous or chemically-induced tumours. This augmentation could only detected when total lytic activity was considered: when NK activity was measured merely on a cell-for-cell basis, it often appeared to be depressed in such animals, in agreement with previous reports. However, with one rapidly metastasizing spontaneous tumour, a real depression of both spleen and blood NK activity was found. Small inocula of cells from non-immunogenic spontaneous mammary tumours or from other non-immunogenic spontaneous tumours caused no early increase in systemic NK activity when injected into the mammary pad, a site where spontaneous tumours frequently arise. However, cells from one immunogenic spontaneous tumour and 2/3 immunogenic chemically-induced tumours did occasionally stimulate significant early increases in NK activity when placed at this site. Early changes in peritoneal exudate NK activity were also investigated using small inocula of these tumours injected intraperitoneally. Augmentation of NK activity occurred with a 3-fold greater frequency following inoculation with immunogenic tumour cells than with non-immunogenic cells in this system. It can be concluded from these studies that: (1) spontaneous tumours do not selectively arise in members of an inbred strain with subnormal NK activity; (2) most large tumours in rats stimulate rather than depress NK activity; (3) early boosting of NK activity by small inocula of tumour cells placed in the mammary pad does not occur with non-immunogenic spontaneous tumours; (4) early boosting of NK activity in the peritoneal site does occur with non-immunogenic tumours, but with a very low frequency. The latter findings suggest that developing spontaneous tumours are unlikely to stimulate the NK system, and emphasize the importance of using syngeneic, spontaneous tumours for studying tumour-host relationships in animals.

Increased susceptibility to cytomegalovirus infection in beige mutant mice

Mice homozygous for the beige gene (bg/bg) are a homologue of the Chédiak-Higashi syndrome of man and are known to be selectively defective in natural killer (NK) cells. We have compared the susceptibility of bg/bg and bg/+ C57BL/6J mice to infection with murine cytomegalovirus (MCMV). Beige mice are more susceptible to lethal infection and develop 33- to 43-fold higher virus titers in the liver, spleen, and kidney than do bg/+ mice after a sublethal infection, although virus replication is the same in vitro in cultured fibroblasts or epithelial cells from these mice. Inoculation with a sublethal dose of virus stimulates a NK cell response, although this is lower in bg/bg mice despite higher titers of interferon type 1 than in bg/+. A dose of MCMV that is lethal only to bg/bg augments cytotoxicity within 12 hr in bg/+ mice, whereas cytotoxicity in bg/bg remains very low. In bone marrow chimeras, recipients of bg/bg marrow were more susceptible to MCMV and had lower NK cell responses after virus inoculation than did recipients of marrow from bg/+ donors. The greater susceptibility of beige mice to the virus suggests that NK cells may contribute to resistance early in McMV infection.

Factors affecting stimulation of natural cytotoxicity to a rat lymphoma by Corynebacterium parvum

Differences were seen in the ability of 2 strains of C. parvum to augment cytotoxicity attributable to NK cells towards a rat lymphoma. Furthermore, 2 batches of the same strain of C. parvum prepared by different methods also differed in their ability to augment cytotoxicity. Other factors influencing cytotoxicity were dose, route of inoculation and time after injection at which the assay was performed. Although all preparations of C. parvum augmented the cytotoxicity of peritoneal-exudate cells when injected i.p., only the most stimulatory preparation consistently augmented splenic cytotoxicity when given by this route. I.v. administration of 1 mg of C. parvum produced peak levels of splenic cytotoxicity 2-3 days later, but this response was strictly dose-dependent, since 1 microgram depressed splenic cytotoxicity. This dose-dependent effect also extended to ADCC, since 1 mg stimulated cytotoxicity towards antibody-coated P815 cells, whilst 1 microgram depressed it in a manner similar to its effect on natural cytotoxicity. Whilst the cytotoxic cells of stimulated rats closely resembled the NK cells of normal rats, BN rats responded differently to C. parvum from W/Fu or WAG rats, in that marked lysis of P815 or RBL-5 cells was observed, though these targets are usually resistant to lysis by rat NK cells in short-term assays.

Augmentation of cell-mediated cytotoxicity to a rat lymphoma. III. In vitro stimulation of natural killer cells by a soluble factor

The in vitro cytotoxicity of rat natural killer cells was augmented by the incubation of normal spleen cells with a soluble factor derived from the 24-h culture of spleen cells and various tumour cells. Cytotoxicity was augmented approximately 4-, 3- or 2-fold depending on whether the spleen cells were incubated with the factor for 18 or 3 h or during the course of the cytotoxicity assay respectively. The factor was produced in cultures containing syngeneic, allogeneic or xenogeneic tumours and no correlation was observed between the ability of tumour cells to induce the production of the factor and their susceptibility to lysis in the 4-h cytotoxicity assay. The factor was produced in cultures of spleen cells of several rat strains, and it stimulated the cytotoxicity of syngeneic and allogeneic spleen cells. The cells responsive to stimulation closely resembled NK cells of normal rats. Culture supernatants containing the stimulatory factor possessed anti-viral activity, and evidence suggested that NK cells were stimulated by a factor resembling a type-I interferon. The relevance of these findings to the stimulation of NK cells by tumours in vivo is discussed.

Tumour-related changes in natural killer cell activity in melanoma patients. Influence of stage of disease, tumour thickness and age of patients

The influence of tumour growth on the natural killer (NK) activity of melanoma patients was examined by analysis of NK activity in 51Cr release assays before and at intervals after surgical removal of localized melanoma. In patients with Stage I and II melanoma, removal of the tumour was associated with changes in the level of NK activity which were not detected in patients who had surgery for skin graft after previous removal of the primary melanoma. The changes in NK activity after removal of melanoma were however different in patients with Stage I compared to Stage II melanoma. In the former, NK activity which appeared specifically directed toward melanoma cells was maximal 2-4 weeks after removal of the tumour and then decreased to normal levels. The NK activity after surgery was directly related to the thickness of the tumour. In patients with Stage II melanoma, NK activity did not increase but fell to low levels after removal of the tumour. The level of NK activity in these patients was not related to the thickness of their primary melanoma. In patients with Stage I and II melanoma the NK activity against melanoma cells showed a significant increase with age. The reason for the different sequence of changes in NK activity after removal of melanoma in the two patient groups is unknown. It is suggested however that the differences observed in patients with Stage II melanoma may reflect differences in the tumour or host response which contributed to the spread of the tumour to regional lymph nodes in these patients.

Augmentation of cell-mediated cytotoxicity to a rat lymphoma. II. Characterization of the non-T cytotoxic cells stimulated in vivo by tumour cells as natural killer cells

A variety of tumours injected into rats were found to rapidly stimulate cytotoxicity which was similar to naturally-occurring cytotoxicity of normal rats. Cytotoxic cells from the spleen and peritoneal cavity closely resembled NK cells in their lytic specificity and cell-surface characteristics. Thus, although cytotoxicity could be stimulated "non-specifically" with tumours which were resistant to lysis in vitro by NK cells, the cytotoxic cells exhibited patterns of specificity against a panel of target cells in direct lysis or competitive inhibition assays which were similar to those of NK cells from normal rats. These cells also closely resembled NK cells in being largely non-adherent, non-T cells, and in exhibiting a similar heterogeneity in the expression of Fc receptors. Thus, cytotoxicity which was augmented shortly after tumour inoculation appeared to be attributable to NK cells. However, whilst the majority of NK cells from normal or tumour-inoculated rats shared these properties, significant heterogeneity was observed. Minor populations of cytotoxic cells were adherent, were lysed by a heterologous anti-T-cell antiserum and complement and did not express an Fc receptor, although it was not determined whether the same subpopulation possessed all three characteristics.