Suppressor cells of the human NK activity: characterization of the cells and mechanism of action

Prostaglandins from human T suppressor/cytotoxic cells modulate natural killer antibacterial activity

We have recently described potent antibacterial activity of purified human NK cells. Here we show that this function is regulated by T cytotoxic/suppressor CD8+ cells. Thus, coculture of NK and CD8+ cells for 3 h or longer times abrogated the expression of the NK antibacterial activity, and of two activation markers IL-2R and transferrin receptor (Tf-R). The suppressive activity was mediated by PGE2 as demonstrated by direct PGE2 determination in CD8+ cell free supernatants, and by inhibition of CD8+ cell suppression with indomethacin or piroxicam in vitro. We also found that resting T cytotoxic/suppressor cells purified by negative selection produce higher amounts of PGE2 than adherent cells like monocytes and macrophages, and that these concentration levels are in the range of concentrations known to suppress a significant number of in vitro immunologic functions.

Suppression of natural killer cell activity in young and old mice

Spleen cells from female mice of the recombinant inbred strain BPS lack natural killer (NK) cytolytic activity, and can suppress the cytolytic activity of normal NK effector cells. The suppressor cells are not typical B cells, T cells, macrophages, or NK cells; they lack the characteristics and surface markers of each of these cell types. In BPS mice, suppressor cell activity is a dominant and significant characteristic of spleen cells at every age tested (2 weeks to 18 months). In other strains of mice which are normally classified as high-responders in NK assays, such as the C57BL strain, these suppressor cells are less prominent but can be detected when separated (on the basis of their higher density) from other spleen cell populations. As mice of the high-responder strains age, however, the suppressor cells become a significant part of the spleen cell population.

Natural killer-cell activity, interferon-alpha 2 production, and interleukin-2 production in cyclosporine-treated and conventionally immunosuppressed human allograft recipients

Natural killer (NK) activity, interferon (IFN)-alpha production, and interleukin-2 (IL-2) production were measured in renal transplant recipients undergoing immunosuppression with either azathioprine and steroids (Az + P) or cyclosporine (CyA). Overall, both IFN-alpha production and IL-2 production were impaired in these two groups compared with identical studies in healthy individuals. However, on the basis of control data these two patient groups were divided into those with "normal" NK activity and those with "low" NK activity. In the CyA group those with a low NK reaction produced less IL-2 and IFN-alpha than those with normal NK activity. No such relationship between cytokine production and NK activity was discerned in the Az + P group. These data conflict with in vitro studies, which have failed to demonstrate any effect of CyA on IFN-alpha production. In addition, they suggest that whereas cyclosporine influences NK activity in vivo by inhibiting cytokine production, other factors may play a role in impairing NK activity in conventionally immunosuppressed patients.

Sensitivity of human fetal hemopoietic cells to NK cell-mediated lysis

Hemopoietic cells from human fetal livers at 11 to 18 weeks of gestational age were studied as to whether they were sensitive to adult and autologous fetal NK cells. Cell line K562 was used as control target in the 51Cr release assay and in the cold target competition assay. Adult peripheral blood NK cells did not kill liver-derived hemopoietic cells of four fetuses tested. Neither did fetal liver cells, whether or not expressing spontaneous cytotoxicity against K562 cells, destroy autologous hemopoietic liver cells. Hemopoietic liver cells from six fetuses were studied in the cold target competition assay. Liver cells of two fetuses clearly competed with lysis of K562 cells by adult NK cells. Thymus cells from one 18 week-old fetus had a weak capacity to compete with lysis of K562 cells by adult cells, whereas cells from the spleen and liver of the same fetus did not. It is concluded that early fetal liver hemopoietic cells are not susceptible to lysis by NK cells but an interaction between fetal cells and NK effector cells results in a depressed NK cell activity against NK-sensitive target cells.

The organization of cell populations within lymph nodes: their origin, life history and functional relationships

The normal lymph node comprises a superficial cortex, a deep cortex or paracortex and a medulla. In each of these regions there are three kinds of spaces: an intralymphatic space, an intravascular space and an extravascular space or interstitium. Both the vascular endothelium and the lymphatic endothelium are specialized in these different regions. The cell types in lymph nodes comprise lymphoid cells, accessory or non-lymphoid cells and stromal cells, and within these cell types a number of different sub-types can now be identified by means of enzyme- and immunocytochemistry. Based predominantly on experimental studies, the origin, migratory patterns, localization, inter-relationships and interactions between these various cells are reviewed.

Cells responsible for tumor surveillance in man: effects of radiotherapy, chemotherapy, and biologic response modifiers

Currently, the most probable theory of tumor surveillance is neither the existence of any tumor-specific, antigen-dependent, T-cell-mediated cytotoxic effect that could eliminate spontaneous tumors in man and that could be used for some kind of vaccination against tumors, nor the complete absence of any surveillance or defense systems against tumors. What is probable is the cooperation of a number of antigen-independent, relatively weakly cytotoxic or possibly only cytostatic humoral and cellular effects, including nutritional immunity, tumor necrosis factor, certain cytokines, and the cytotoxic effects mediated by macrophages, NK cells, NK-like cells, and certain stimulated T-cells. One question remaining to be solved is why these antigen-independent effects do not attack normal cells. A number of plausible hypotheses are discussed. The hypothetical surveillance system is modulated both by traditional cancer treatment and by attempts at immunomodulation. Radiotherapy reduced the T-helper cell function for almost a decade, but not those of macrophages or NK cells. T-cell changes have no prognostic implication, supporting, perhaps, the suggestion of a major role for macrophages and NK cells. Cyclic adjuvant chemotherapy reduces the peripheral lymphocyte population and several lymphocyte functions but not NK activity. Most of the parameters were normalized some years following treatment, but NK activity remained elevated and Th/Ts cell ratio was still decreased. This might possibly be taken to support the surveillance role of NK cells. Bestatin increases the frequency of lymphocytes forming rosettes with sheep red blood cells (but not their mitogenic responses), enhances NK activity, and augments the phagocytic capacity of granulocytes and monocytes (but not their cytotoxic activity). Improved survival with Bestatin treatment following chemotherapy has been observed in patients with melanoma Stages 1b and II and in patients with acute nonlymphatic leukemia, where BCG also seems active, although possibly only in patient groups with less than 49% complete remissions.

Immune function in chronic active Epstein-Barr virus infection

The spectrum of illness attributed to Epstein-Barr virus (EBV) includes patients with symptoms persisting for more than 1 year without any other obvious underlying disease. High titers of antibodies to EBV, either IgG antiviral capsid antigen or anti-early antigen, can be demonstrated. In this study, 13 patients diagnosed as having chronic active EBV infection were examined to determine aspects of their immunologic status. Morphological examination and fluorescent antibody analysis revealed no abnormalities in the phenotypes of peripheral blood white cells present in these patients. Compared to those from healthy control individuals, mononuclear cells from the patients showed a markedly depressed ability to produce both interleukin-2 and interferon after stimulation with mitogen and a phorbol ester. Studies of natural killer (NK) cell activity revealed that unfractionated mononuclear cells from patients with chronic active EBV infection were significantly lower in killing activity compared to the control group. Fractionation procedures to enrich for large granular lymphocytes resulted in an increase in NK activity for all individuals, but killing activity still remained slightly lower in the patients than in the control group. The dysfunctions which were found in patients with chronic active EBV infection may reflect a primary defect in natural immune functions of the patients predisposing them to a chronic or intermittent clinical disease rather than a self-limiting illness. Alternatively, the abnormalities detected in these experiments may be a result of the viral infection itself.