RNK-16 cells, rat leukemia cells with features of natural killer (NK) cells, were adapted for growth in vitro and used to examine the mechanism of NK-cell activation. Contact of RNK-16 cells with tumor cells (YAC-1) that are lysed by NK cells, but not with resistant tumor cells (EL-4, K562), led to an increase in inositol trisphosphate (InsP3), a Ca2+-mobilizing messenger. A similar increase in InsP3 could be elicited in RNK-16 cells by monoclonal antibody OX-34, when the antibody was crosslinked by F(ab')2 fragments ofgoat antibodies to mouse immunoglobulin. This reaction was accompanied by an increase in the concentration of cytoplasmic free calcium Ca2+, due primarily to the release of Cal+ from intracellular stores. In contrast to the stimulatory effects of crosslinked OX-34, OX-34 alone did not affect the levels of either InsP3 or cytoplasmic free Ca2 . Moreover, OX-34 alone blocked the generation of InsP3 by RNK-16 cells in response to YAC-1 cells and prevented target-cell killing. These findings demonstrate that OX-34 identifies a structure on the surface of RNK-16 cells that can stimulate the generation of InsP3, and they suggest that this structure can regulate signal transduction during target-cell recognition by NK cells.
Anomalous killer cells are Thy-1(+) blasts that are cytolytic to the natural killer (NK)-sensitive lymphoma YAC-1, and that can be detected early (day 3-4) in the period preceeding the allospecific cytotoxic T lymphocyte (CTL) response in (CBA x A)F1 {arrow} C57B1 mixed leukocyte culture (MLC). We have investigated the origin and nature of anomalous killing (AK), with special emphasis on its relation to NK-and allospecific CTL-activity. AK was shown to be distinct from the previously described "NK(c)-cells" induced by cultivation in fetal calf serum (FCS)-supplemented medium when these two reactivities were examined in parallel. AK was detected in either FCS- or normal mouse serum (NMS)-supplemented allogeneic MLC, indicating that the response was not dependent on mitogenic or antigenic properties of heterologous serum. In addition to several H-2-incompatible combinations, AK was also observed in an Mls-incompatible (but H-2 compatible) and two F(1)- antiparental MLC responder/stimulator combinations. AK cells showed a similar selectivity pattern to NK cells, as demonstrated in cold target inhibition and direct cytotoxicity assays using variant or interferon-modulated YAC-1 cells with low expression of NK target structures. The AK-cells were NK- 1.2(-/weak). Thy-l.2(+), although they seem to be derived from non-adherent radiosensitive cells which are closely related, if not identical, to NK-cells (NK-1.2(+). Thy-l.2(-/weak)), as they could not be readily induced in responder populations with low NK-activity but normal allospecific CTL potential. Conversely, an in vivo thymectomy protocol or treatment of normal spleen cells with monoclonal anti-Thy-1.2 + C reduced the allospecific CTL response drastically but did not affect the AK response. Anomalous killers were not observed when MLC were prepared with responder as well as stimulator cells devoid of mature T cells. In such a combination, the AK response could be partially restored by the addition of irradiated +/nu (but not nu/nu) responder cells to the cultures. When normal (non-nude) spleen cells were used as responders, induction of AK did not require the presence of T cells in the stimulator population, whereas the removal of adherent and phagocytic cells from stimulators abrogated the response.
Taken together, the results suggest that AK represents activation, blast transformation, and surface marker modulation of NK cells induced by alloantigen-stimulated T cells, resulting in Thy-1(+) cytolytic cells with similar properties to those described for NK lines, Although AK cells may be regarded as a more T cell-like NK phenotype, their induction is neither necessary, nor sufficient for generation of specific CTL in MLC.
Human mitomycin C-treated PBL were mixed with cells of an NK sensitive hybrid cell line (PUTKO-I). A fraction of tumor cells survived this treatment and could be recovered from the cultures. These surviving cells were completely NK-resistant and this property persisted for 2-3 weeks after cultivation in fresh medium. Treatment of a clone (C13) of PUTKO-I with PBL-PUTKO mixed lymphocyte-tumor-cell culture (MLTC) supernatants resulted in a marked reduction in NK sensitivity after 8-12 h of treatment. The kinetics of induction of NK resistance by MLTC supernatants was similar to that of purified IFN-gamma and was faster than for IFN-alpha. The active component in the supernatants was characterized as a mixture of IFN-gamma and IFN-alpha based on neutralization of activity with specific antisera. The role of mycoplasma contamination was investigated and it was found that cell lines free of detectable mycoplasma stimulated production of NK-protective activity by PBL and this activity was neutralized by anti-IFN-gamma serum. Separation of PBL on discontinuous Percoll gradients demonstrated a correlation between the NK activity of cell fractions and their ability to produce IFN in response to tumor cells. Taken together, the selection-dependent variations in NK sensitivity, the kinetics of IFN production and induction of resistance suggest that tumor cells may be able to escape elimination by NK cells due to protection by IFN produced by the effector-cell-containing population.
Immunocompetent C57BL/6J mice and beige mice (which are deficient in natural killer cells) were infected with Giardia muris. Both types of mice cleared G. muris infection at similar rates. This observation suggests that clearance of G. muris parasites from the mouse intestine is not mediated by natural killer cells.
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