NK cell-target interactions: approaches towards definition of recognition structures

Effects of the immunomodulator PSK on growth of human prostate adenocarcinoma in immunodeficient mice

Tumor growth alterations were studied using an immunomodulator, PSK. Four human prostate tumor lines were grown in two types of immunodeficient mice. Two of the lines were selected because they are able to metastasize to lungs in host animals. Outbred NIH Swiss athymic mice having normal natural killer cells and athymic Beige mice deficient in natural killer cells were used as animal hosts. PSK treatment was given to tumor-bearing hosts to some animals soon after solid tumors were injected and to others after solid tumors were well-established. Low dose cyclophosphamide was given to some animals to decrease host natural killer cells and polyinosinic-polycytidylic acid (poly I:C) was given to other animals to increase natural killer cell activity. Measurement of tumor doubling times, host survival and metastatic capabilities showed that either poly I:C or PSK treatment in NIH Swiss animals soon after tumor cells were injected significantly increased tumor doubling times and host survival and decreased the incidence and number of metastatic lung lesions. Two of the tumor lines incapable of metastasizing in NIH Swiss mice were metastatic in the Beige athymic, natural killer-cell-deficient animals.

Growth and metastatic behavior of human tumor cells implanted into nude and beige nude mice

The growth and metastatic behavior of several human tumor lines grown in adult nude mice, nude mice pretreated with antiserum against asialo GM1 glycoprotein, and beige nude mice were studied. The cell lines were all injected s.c. and i.v. A human colon carcinoma line was also injected into the spleen, and two human renal carcinoma lines were injected into renal subcapsule. All the tumor lines grew as fast or faster in adult nude mice compared with beige nude mice. There were no discernible differences in the production of experimental lung metastasis among the three groups of mice, but human colorectal carcinoma cells and human renal carcinoma cells produced more metastases in nude mice than in beige nude mice after intrasplenic or renal subcapsule injection, respectively. In vitro cytotoxicity assays confirmed that adult nude mice had high levels of natural killer (NK) cell activity whereas nude mice pretreated with anti-asialo GM1 serum and beige nude mice did not. The in vitro NK cell activity of nude mice was demonstrable against mouse lymphoma cells but not against human leukemia cells which were sensitive to lysis by human NK cells. These results suggest that the implantation of human tumor cells into beige nude mice, which are deficient in NK cell activity does not provide an advantageous model for the study of growth and metastasis of human neoplasms.

Specific inhibition of human natural killer cell-mediated cytotoxicity by sialic acid and sialo-oligosaccharides

We have tried to identify carbohydrate structures involved in recognition and/or lysis of K562 target cells by human natural killer (NK) cells. Inhibition studies were performed with mono-, di- and trisaccharides, and with glycopeptides and glycoproteins of known carbohydrate composition. When tested with various monosaccharides, lysis of K562 cells was inhibited only by N-acetylneuraminic acid (NeuAc). Di- and trisaccharides and glycopeptides containing NeuAc or N-glycolylneuraminic acid (NeuGc) all inhibited NK cell-mediated lysis. Among the non-sialylated carbohydrates tested, only Gal beta(1----3)GalNAcol was effective. The inhibitory capacity of sialylated compounds appeared to be dependent on the linkage type of the sialic acid residue; carbohydrates containing alpha(2----6)-linked sialic acids were more potent inhibitors than their alpha(2----3) isomers. Also the sugar to which the sialic acid residue was attached was of importance, NeuAc alpha(2----6)GalNAcol being more effective than NeuAc alpha(2----6)Gal beta 1----R (where R = glucose or oligosaccharide-peptide). Sialylated compounds and free sialic acid had minor or no effects on cell-mediated cytotoxicity by allo-sensitized cytotoxic T lymphocytes. The conjugation of target cells and NK effector cells was not inhibited by carbohydrates that effectively blocked the cytolytic response. These results may indicate that cell-surface carbohydrates containing alpha(2----6)-linked sialic acid are crucial structures in a post-binding event in NK-cell-mediated lysis.

Similarity between the interleukin 1 receptors on a murine T-lymphoma cell line and on a murine fibroblast cell line

Interleukin 1 beta (IL-1 beta), one of two different polypeptide hormones with interleukin 1 (IL-1) biological activity, produced by activated human monocytes, is a 17.5-kDa protein. IL-1 beta binds specifically to a variety of cells; the cellular distribution of binding is consistent with reported biological responsiveness. In this report we show that two unrelated, but IL-1-responsive, cell lines, LBRM-33-1A5, a T-lymphoma line, and BALB/3T3, a fibroblast line, bind 125I-labeled IL-1 beta via similar plasma membrane receptor molecules. The T-lymphoma cells possess 238 +/- 16 plasma membrane receptors per cell and bind 125I-labeled IL-1 beta with an affinity of 3.6 +/- 0.9 X 10(9) M-1. The IL-1 receptor has a molecular size of approximately equal to 79.5 kDa, as estimated by affinity cross-linking. The fibroblasts possess 4.8 +/- 0.5 X 10(3) IL-1 receptors per cell and bind 125I-labeled IL-1 beta with an affinity of 2.6 +/- 0.5 X 10(9) M-1. The molecular size of the receptor molecule on the fibroblasts is approximately equal to 78 kDa. Despite the similarity in the characteristics of the ligand-receptor system on the two different cell types, the biological responses of the two cell types to IL-1 beta occur at IL-1 beta concentrations that differ by four orders of magnitude.

Rationale and methods for the use of nude mice to study the biology and therapy of human cancer metastasis

Human neoplasms are biologically heterogeneous. The extensive cellular diversity found in malignant neoplasms is generated by the rapid emergence of clonal subpopulations of tumor cells with different properties that include invasion, metastasis and responsiveness to treatment. Studies in rodent systems have indicated that cancer metastases can be clonal in their origin and that different metastases can originate from different progenitor cells from the primary tumor. This metastatic heterogeneity of tumor cells has many ramifications for studies of tumor biology, in general, and studies of therapy, in particular. The heterogeneous nature of metastatic human neoplasms can now be studied under defined conditions in healthy athymic nude mice. The neoplasms must be free of mouse pathogens and the mice must be kept in specific-pathogen-free conditions. Careful consideration must be given to the intimate tumor-host relationship for each tumor system studied, because the metastatic potential of human neoplasms can vary with the site of implantation into nude mice. Several methods for studying the biology of human neoplasms in the nude mouse are described as well as techniques to assure the success of these studies. The data show that the healthy young nude mouse can be a useful in vivo model for ascertaining the metastatic potential of human neoplasms, for selecting and maintaining cell variants of high metastatic potential from heterogeneous human tumors, and for studying therapeutic agents directed against metastatic cells proliferating in visceral organs.

Quantitative measurement of human interleukin 2 receptor levels with intact and detergent-solubilized human T-cells

2A3 monoclonal antibody (gamma 1, kappa) is a novel high-affinity reagent for detecting the human interleukin 2 (IL-2) receptor. The antibody inhibits IL-2 binding to its receptor and is an antagonist of IL-2 action. Detailed analysis of the mechanism of binding of the IgG, (Fab')2 and Fab' of 2A3 antibody shows that the bivalent species cross-link on the cell surface when bound. Measurements of IL-2 receptor expression on digitonin-permeabilized cells suggest that the intracellular pool of receptors is small. The antibody will bind to IL-2 receptors on glutaraldehyde-fixed cells in the presence of Triton X-100. This property is used in designing an assay for quantitative measurements of IL-2 receptor concn in solution. This assay can be used to monitor receptor protein during purification to homogeneity.

Detection and characterization of high affinity plasma membrane receptors for human interleukin 1

Interleukin 1 (IL-1) is a polypeptide hormone that acts as a central mediator of inflammation. Since IL-1 action is presumably mediated by specific cell surface receptor(s), we have characterized the binding of this hormone to cells. Purified human IL-1 was labeled to high specific activity with 125I, using Bolton-Hunter reagent. The labeled protein binds specifically to LBRM-33-1A5 (a murine T lymphoma line previously shown to produce IL-2 in response to phytohemagglutinin and IL-1) with an affinity of approximately 0.2-2 X 10(10)/M and, at saturation, to approximately 500 receptors per cell, on intact cells at 8 degrees C in the presence of sodium azide. The affinity of unmodified IL-1 for the murine plasma membrane receptor is 0.9-2 X 10(10)/M, as measured by the inhibition of 125I-IL-1 binding. The murine receptor specificity has been confirmed by demonstrating that, among a series of 12 polypeptide hormones, only IL-1 inhibits 125I-IL-1 binding to LBRM-33-1A5 cells. Treatment of surface-bound 125I-IL-1 with bivalent water-soluble crosslinkers identified a membrane polypeptide of Mr 79,500 to which IL-1 is crosslinked. A variety of cell types have been surveyed for the capacity to bind 125I-IL-1 specifically. The presence of specific binding correlates with the capacity of the cells tested to respond to IL-1. Our results indicate that the biological effects of the polypeptide hormone IL-1 are mediated by high affinity plasma membrane receptors. The identification of these receptors should provide valuable insight into the apparently diverse biological activities of IL-1.

Purification and chemical characterization of the receptor for interleukin 2 from activated human T lymphocytes and from a human T-cell lymphoma cell line

The cell surface receptor for interleukin 2 plays a central role in the biology of this T-cell growth factor. A combination of affinity chromatography, high-performance liquid chromatography, and NH2-terminal protein sequencing was used to purify and chemically characterize the interleukin 2 receptor both from phytohemagglutinin-activated T cells and from the human T-cell lymphoma cell line HuT-102. The receptor isolated from HuT-102 cells was purified 16,000-fold to homogeneity as evidenced by (i) a final specific activity close to the theoretical specific activity of 18,182 fmol of receptor per microgram of protein, (ii) a single band on polyacrylamide gel electrophoresis with an Mr of 55,000, and (iii) a unique, unambiguous NH2-terminal protein sequence. The receptor purified from phytohemagglutinin-activated T lymphocytes had an Mr of 60,000 but it had the same NH2-terminal protein sequence.

Neoplastic cells as targets of spontaneously cytotoxic lymphocytes: studies with natural killer-like cell lines

Native natural killer (NK) cells comprise a heterogeneous family of lymphocytes distributed among several organs, which display spontaneous cytotoxic reactions directed against a broad range of tumor targets. In these studies, murine cell lines have been established in vitro following the selective expansion of bone marrow- and spleen-derived killer progenitors in culture medium supplemented with interleukin-2. Several clones of independent origin have been characterized in order to determine the extent of their phenotypic and functional diversity. With few exceptions most of them were found to be highly effective in lysing a variety of tumor cell lines, to share common cell surface alloantigens, lectin-binding receptors, and cytochemical markers. The presence of prominent azurophilic cytoplasmic granules is the most characteristic ultrastructural feature of these cells. In attempting to elucidate the nature of membrane components specifically recognized by NK cells we compared several isogenic tumor cell variants selected on the basis of their differential NK susceptibility, immunogenicity, metastatic potential or resistance to cytotoxic plant lectins. Sialylated glycoconjugates exposed on the external face of the tumor cell membrane appear to be essential determinants in the interaction between NK cells and their targets. Permanent cell lines retaining most of the functional attributes of endogenous NK cells may prove instrumental in understanding their role during tumor progression.

Natural cytotoxicity in lymphatic metastasis. I. In vitro studies using the rat tumor BSp73 and its variants

Serial transplantation of primary BSp73 ascites cells to a subcutaneous (SC) site gave rise to the appearance of two solid variants differing in their capacity to metastasize via the lymphatics. Tissue cultures derived from variant AS (nonmetastasizing) showed epithelioid morphology, while cultures derived from variant ASML (metastatic) showed spherical morphology. Upon cloning, both variants proved to be operationally homogeneous. Susceptibility of cultured BSp73 cells to NK and macrophage-mediated cytotoxicity was closely correlated to morphology, inasmuch as epithelioid cells were susceptible, while spherical cells were resistant, to lysis. With stimulated effector cells a general increase in cytotoxicity was observed, but epithelioid cells still showed a higher susceptibility level. Resistance of ASML-type cells to natural cytotoxicity was not due to the lack of recognition structures or to a general increase in the mechanical stability of spherical cells. This was concluded from cold target inhibition and from hypotonic shock treatment experiments, respectively.

Natural killer cells: artifact to reality: an odyssey in biology

The biology of the natural killer cell system is being investigated by many different laboratories using multiple approaches. The rationale for these investigations is the experimental evidence that NK cells play some role in inhibiting tumor growth and metastasis, convey some protective immunity and may be operative in control of differentiation from fetal life to adulthood. Thus, a survey of the literature reveals a multiplicity of studies examining many of these potential roles for NK cells. This review will attempt to summarize some of the findings critical to an understanding of the role NK cells play in immunophysiology and in immune reactions to various diseases. Even after ten years of study, the whole system of 'natural' reactivity remains difficult to define. The evidence available would indicate that the NK system while incompletely understood, may be manipulated in favor of the host when threatened by infectious or neoplastic disorders.