Natural killer cell activity and ultrastructure in myeloproliferative reactions in infants with Down's syndrome.

In some infants with Down's syndrome, the circulating mononuclear population, when viewed with conventional and electron microscopy, contains many cells that closely resemble leukemic blast cells. In contrast with true leukemia, however, most of these infants with the "leukemia-like reaction in Down's syndrome" (LLR-DS) enter spontaneous remissions. We therefore investigated the natural resistance of such infants to hematological malignancy in vitro by means of natural killer cell assays. Mean natural killer cell determinations in four infants with LLR-DS were 17.5 +/- 9.2% and 37.6 +/- 18.5% against K-562 and Molt-4 target cells, respectively, at diagnosis. Later, during remission, these values were 34.3 +/- 14.3% against K-562 and 32.2 +/- 15.6% against Molt-4. The mean percentage lysis of Molt-4 both at diagnosis and during remission was greater (p less than 0.05) in LLR-DS than in children with acute lymphocytic leukemia and acute myelogenous leukemia at diagnosis. Natural killer cell activity levels in these LLR-DS patients were similar to levels obtained in other infants with Down's syndrome who were hematologically normal, as well as levels obtained in normal control specimens. Two of these LLR-DS patients progressively developed acute myelogenous leukemia with ultrastructural abnormalities several months later; one of these also developed another karyotype abnormality. Both remain in long-term remission exceeding 48 months.

Decreased natural killer cell activity in children with untreated acute leukemia.

Natural killer cell activity was evaluated in children with acute lymphocytic and acute myelogenous leukemia. Peripheral blood mononuclear cells isolated at the time of diagnosis and before initiation of therapy were mixed with 51Cr-labeled K562 or MOLT-4 target cells at a ratio of 100:1. In 13 consecutive cases of acute lymphocytic leukemia, the mean percentage of lysis of K562 cells (15.0%) was significantly below that of adult (49.8%) and age-related controls (35.9%). A similar pattern was observed against MOLT-4 targets (acute lymphocytic leukemia, 11.3%; adults, 39.8%; and pediatric controls, 28.4%). The mean activity in 8 cases of acute myelogenous leukemia was also markedly reduced (6.8% versus K562 and 6.0% versus MOLT-4). Linear regression analyses of white blood cell, lymphocyte, and leukemia blast counts failed to demonstrate any correlation between peripheral cell counts and natural killer cell activity. Thus, it would not appear that the observed decrease in lysis was due merely to dilution of effectors with blasts. The lytic activity of cells isolated from patient blood was significantly lower than that from cells isolated from an equal volume of blood from a normal adult. These results suggest that the decreased natural killer cell activity is not explained by simple dilution. Instead, they indicate an absolute decrease in lytic potential. Additional experiments have precluded suppressor cell involvement and competitive inhibition of blasts with target cells as possible causes for depressed lysis.

Elevation of natural killer activity and nonspecific immunity following injection of Listeria cell walls.

Mice given a single intraperitoneal injection of cell walls from Listeria monocytogenes (LCW) prior to challenge with Candida albicans or a mammary carcinoma showed significantly increased survival compared to saline injected controls. The cell walls were mitogenic for spleen cells in vitro. Levels of stimulation were lower than for Con A and PHA but comparable to those induced by LPS. Peritoneal exudative cells, but not spleen cells, harvested from mice injected with LCW showed significant elevation of natural killer (NK) cell activity as early as 1 day following injection. NK activity remained elevated for 10 days and then returned to normal levels by day 145. Macrophage phagocytic and tumorcidal activity in vitro did not appear stimulated. In overall comparison to commercial mitogens, LCW had lower levels of activity measured in vitro but equivalent or higher in vivo levels of protection.

lack of suppressor cell activity for natural killer cells in infant, aged and a low responder strain of mice.

We have examined the reported role of suppressor cells in the regulation of NK activity in mice with naturally low NK activity (infant and aged (C57 X A)F1 hybrids (CAF1) and low responder strain AKR mice). Possible suppressor activity was assayed by mixing, at a 1 : 1 ratio, spleen cells from low activity mice with spleen effector cells from normally active 8 to 10 wk old CAF1 mice. The lytic activity of the mixture was compared with the activity of effector cells diluted with medium alone or diluted 1 : 1 with "non-suppressor" population which served as a control for nonspecific decreases in lysis. The control or "filler" cells employed were suspensions of adult CAF1 thymus, thymus from adult mice exposed to 2,000 R, and adult CAF1 spleen cells cultured for 24 hours, a procedure that depleted NK activity. In no case was the activity observed in the presumed suppressor-effector mixture significantly lower than that observed in the filler-effector cell mixtures. Thus, in infant (1 to 2 wk) and aged (12 to 18 mo) CAF1 mice and in 8 to 10 wk old AKR mice, we found no evidence for specific cell-mediated suppression of natural cytotoxicity.

Augmentation of natural killer cell activity in spleens of infant, aged, and low responder strain mice by Corynebacterium parvum.

Murine natural killer (NK) cell activity is both age- and strain-dependent. NK activity does not appear in murine spleen cells until three weeks after birth. Activity peaks at approximately 10 weeks, decreasing thereafter with mice over one year old showing significantly reduced levels. Mice showing low or no NK activity because of age (aged and infant mice, respectively) can be stimulated to show significant levels of NK lysis by i.p. injection of formalin killed Corynebacterium parvum (CP). In addition, CP treatment is also capable of increasing NK activity in mice from the normally low responding AKR strain. The NK activity induced or stimulated by CP appears to be like normal NK reactivity in that it is not decreased by removal of T-cells or adherent cells. Thus, in addition to increasing NK activity in normally responsive mice, CP is capable of augmenting NK activity in mice which normally show low or no levels of NK lysis.

Comparative effects of different strains of Corynebacterium parvum on natural cell-mediated cytotoxicity.

Because there are conflicting reports regarding the effects of Corynebacterium parvum (CP) on natural killer (NK) cell activity, several different strains of CP were compared. In replicate experiments, age- and sex-matched mice received 0.25-mg i.p. injections of one of four types of CP; formalin-killed strain 6134; heat-killed strain 6134; formalin-killed strain 5888 (actually Corynebacterium granulosum); or formalin-killed CP from the Pasteur Institute. At various days thereafter, two to three mice from each group were sacrificed to determine spleen weight, cellularity, and NK cell activity versus YAC-1 lymphoma cells. The CP from the Pasteur Institute augmented NK cell activity 3 days following injections; however, the activity returned to normal by Day 7 and remained at that level. On the other hand, strain 5888 did not cause as great an increase in lytic activity as did the Pasteur Institute CP at Day 3; but by Day 10 after injection, NK cell levels were above control, and they remained elevated through Day 21. Both the heat-killed and formalin-killed preparations of strain 6134 stimulated NK cell activity initially but resulted in a loss of activity at the later times tested. Experiments done with different doses and routes of injection yielded similar results. Thus, we were able to demonstrate that different types of CP have different effects on NK cell activity in mice and that the general kinetics of these effects were independent of dose or route of administration.

Erythropoietin responsiveness in vivo of Friend virus target cells for transformation and virus replication.

Techniques that allow the selective stimulation of the erythropoietin-responsive cell population in mice with suppressed multipotential hemopoietic stem cells were used to identify (1) the in vivo target cell transformed by Friend virus (FV) into a tumor colony-forming unit and (2) a target cell for FV replication in vivo. Plethoric mice with busulphan-induced reductions in stem cell populations (characterized as colony-forming units) and stimulated erythropoietin-responsive cell compartments were given FV; control groups, not receiving erythropoietin, also received FV. A comparison of the number of target cells transformed in each group provided evidence identifying the ERC as the in vivo compartment in which the target cell detected by tumor colony formation resides. Differences in plasma virus titers revealed that the erythropoietin-responsive cell is also predominantly responsible for the production of FV as measured by focus-forming activity.

In vivo distinction between a target cell for Friend virus (FVP) and murine hematopoietic stem cells.

Busulphan (BU) treatment of DBA/2 mice with hypertransfusion (HT)-induced polycythemia resulted in an ablation of detectable hematopoietic stem cells (CFUS) in pooled marrow from the long bones. Daily injections of erythropoietin (EP) stimulated an EP-responsive population of cells in the absence of detectable CFUS. Mice treated with BU and EP and having HT-induced polycythemia were inoculated with the polycythemia-inducing strain of Friend virus (FVP) and determinations were made for the presence of tumor colony-forming units (tCFU). No change in CFUS/10(6) bone marrow cells was detected as a result of EP treatment. However, tCFU were increased more than 100-fold in HT-BU-EP-treated mice compared with saline-treated controls. The demonstration of tCFU in mice in which CFUS were not detectable indicated that this leukemogenic effect of FVP could occur in the absence of the pluripotent stem cell. Furthermore, the increased numbers of this FVP target cell in the EP-stimulated, BU-treated mice with HT-induced polycythemia supported the model licating the target for this effect in the EP-responsive cell population.