Phospholipid methylation and phospholipase A2 activation in cytotoxicity by human natural killer cells

Development of monoclonal antibodies that specifically interact with necrotic lymphoma cells

The immune system has evolved mechanisms to sense not only microbes, but also necrotic cells. The pattern-recognition receptors in macrophages/dendritic cells that stimulate the acquired immune system are closely associated with danger signaling. In this study monoclonal antibodies (mAbs) that specifically interact with necrotic cells were developed. One IgG1 and two IgM mAbs were established, and they recognized a 80 kDa protein expressed in necrotic, but not live or apoptotic, cells. These mAbs, which serve as a probe for necrosis, facilitate analyses of the role of the immune complex that consists of necrotic cells and Ab and contributes to the formation of the inflammatory milieu induced by necrotic cell death.

Acute Effect of Qi-Training on Natural Killer Cell Subsets and Cytotoxic Activity

This study assesses the effects of Qi-training on natural killer cell cytotoxicity. Nine experimental subjects did 1 h of Qi-training, and 9 control subjects relaxed during the same time. Natural killer cell cytotoxicity increased 60% immediately after Qi-training (p<.01) and returned to the basal level within 2 h after training. Natural killer cell subset number did not change after Qi-training. Natural killer cell cytotoxicity and cell number were not significantly correlated. These data suggest that Qi-training has an acute stimulatory effect on natural killer cell activity, but has no effect on phenotypical changes in the natural killer cell subset.

Cytosolic PLA2 is required for CTL-mediated immunopathology of celiac disease via NKG2D and IL-15

IL-15 and NKG2D promote autoimmunity and celiac disease by arming cytotoxic T lymphocytes (CTLs) to cause tissue destruction. However, the downstream signaling events underlying these functional properties remain unclear. Here, we identify cytosolic phospholipase A₂ (cPLA₂) as a central molecule in NKG2D-mediated cytolysis in CTLs. Furthermore, we report that NKG2D induces, upon recognition of MIC⁺ target cells, the release of arachidonic acid (AA) by CTLs to promote tissue inflammation in association with target killing. Interestingly, IL-15, which licenses NKG2D-mediated lymphokine killer activity in CTLs, cooperates with NKG2D to induce cPLA₂ activation and AA release. Finally, cPLA₂ activation in intraepithelial CTLs of celiac patients provides an in vivo pathophysiological dimension to cPLA₂ activation in CTLs. These results reveal an unrecognized link between NKG2D and tissue inflammation, which may underlie the emerging role of NKG2D in various immunopathological conditions and define new therapeutic targets.

Effects of prednisolone on the systemic release of mediators of cell-mediated cytotoxicity during human endotoxemia

Corticosteroids are widely used for the suppression of cell-mediated cytoxicity. This process is mediated by natural killer cells and cytotoxic T lymphocytes, and their activation can be monitored by levels of the chemokines CXCL9 and CXCL10, the degranulation product granzymes A and B, and by levels of secretory phospholipase A2. The current study aimed to determine the effects of increasing doses of prednisolone on the release of these mediators in healthy humans exposed to LPS. Therefore, 32 healthy men received prednisolone orally at doses of 0, 3, 10, or 30 mg (n = 8 per group) at 2 h before intravenous injection of Escherichia coil LPS (4 ng/kg). Prednisolone dose-dependently attenuated the LPS-induced rises in the plasma concentrations of the chemokines CXCL9 and CXCL10, as well as of granzymes A and B levels. CXCL10 and granzyme B release were most sensitive to prednisolone, with a significant inhibition already achieved at the lowest prednisolone dose (3 mg). The levels of secretory phospholipase A2 were increased after LPS administration but were not significantly affected by prednisolone. This study demonstrates that prednisolone differentially inhibits the systemic release of mediators involved in cell-mediated cytotoxicity in humans in vivo.

Lysophosphatidylcholine produced by the phospholipase A2 isolated from Lachesis muta snake venom modulates natural killer activity as a protein kinase C effector

We have showed that a phospholipase A(2) isolated from Lachesis muta snake venom, denoted LM-PLA(2)-I, had some biological effects. Here, we examined its effects on lymphocytes. Pre-incubation of human peripheral blood lymphocytes with LM-PLA(2)-I plus phosphatidylcholine (PC) stimulated the natural killer (NK) activity. This was accompanied by DNA binding of nuclear transcription factor kappaB and the increase in PKC activity with translocation of the enzyme from the cytoplasma into the plasma membrane. These effects were reproduced when lymphocytes were pre-incubated with commercial lysophosphatidylcholine (LPC) and abolished by stausrosporin or p-bromophenacyl bromide. Evaluation of phosphorylated PKC isoforms showed that pre-incubation with LPC activated the autophosphorylation of the PKCzeta isoform. Taken together, these results confirm that the enzymatic activity of the phospholipase A(2) present in L. muta venom is for the biological activity of the snake venom, and strongly suggest that the LPC produced may be acting as a modulator of PKC isoforms.

Apoptosis-inducing factor of a cytotoxic T cell line: involvement of a secretory phospholipase A2

Natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) kill target cells by the granule-exocytosis pathway and by the engagement of molecules belonging to the tumor necrosis factor family. The involvement of secretory phospholipase A(2) (sPLA(2)) in the cytotoxic process has been proposed in NK cells. However, its molecular identity and intracellular localization remain unknown, and its mechanism of action is poorly understood. Here, we have readdressed this issue by studying the cytotoxic activity of whole cell extracts of a CTL line. We observed that inactivation of the perforin-granzyme pathway at 37 degrees C in the presence of 1 mM Ca(2+) enhanced the ability of CTL extracts to induce apoptosis. This potentiation of cell death was Ca(2+)-dependent, thermo-resistant, and inhibited by 4-bromophenacyl bromide and scalaradial (two inhibitors of sPLA(2)). The involvement of an sPLA(2) was confirmed by blocking the pro-apoptotic activity of the Ca(2+)-treated cell extract with an anti-sPLA(2) polyclonal antibody. By cell fractionation assays, we showed that the pro-apoptotic sPLA(2) was localized in the cytoplasmic fraction but not in perforin-rich granules or plasma membrane fractions. Western blotting analysis revealed the presence of four distinct bands of 56, 29.5, 21, and 15 kDa. The highest molecular weight band was consistent with the expression of a group III sPLA2. Taken together, these data indicate that an apoptosis-inducing sPLA(2) is expressed in the cytosol of a CTL cell line and suggest that it plays an effector role in CTL-mediated cytotoxicity.

Decreased adenylyl cyclase and cAMP-dependent protein kinase activities inhibit the cytotoxic function of human natural killer cells

Natural killer (NK) cells are lymphocytes that are capable of destroying tumor cells and virally infected cells without prior sensitization. Elevation of cyclic 3', 5' adenosine monophosphate (cAMP) levels in NK cells is known to cause dramatic inhibition of NK cytolytic function. However, the effect of lowering cellular levels of cAMP on the cytolytic function of natural killer (NK) cells has not been studied. The current study investigated the effects of inhibiting adenylyl cyclase (AC) or cAMP-dependent protein kinase (PKA) activities on the ability of NK cells to lyse K562 tumor cells, and on the activation of NK-cell phospholipase C (PLC) by tumor targets. Exposure of NK cells to the AC inhibitors MDL-12,330A (MDL) or 2',5',-Dideoxyadenosine (DDA) completely blocked their ability to destroy K562 tumor cells. Further, target-induced stimulation of NK-cell PLC was inhibited by as much as 90% when NK cells were treated with the AC inhibitors. Treatment of NK cells with the PKA inhibitor, H-89, caused essentially complete inhibition of cytotoxic function while decreasing target-induced stimulation of PLC by about 50%. Additionally, exposure to the organotin compound, tributyltin (TBT), which decreases cAMP levels in NK cells (as much as 80%) caused a decrease in cytotoxic function by as much as 90%. These data suggest that decreased levels of cAMP may cause very significant loss of NK cytotoxic function and that this may be mediated by decreased PKA activity. These data coupled with previous work revealing that increased cAMP levels inhibit NK cytotoxic function, suggest that tight regulation of cAMP levels is critical to NK cell function.

Exercise and hypoxia: effects on leukocytes and interleukin-6-shared mechanisms?

Stress-induced immunological reactions to exercise have stimulated much research into stress immunology and neuroimmunology. It has been suggested that exercise can be employed as a model of temporary immunosuppression, which occurs during physical stress, such as hypoxia. Acute exercise and acute hypoxia mediate in principle identical effects on circulating lymphocyte and neutrophil numbers. Thus, during exercise and hypoxia, lymphocytes are recruited to the blood. After the stress, the number of lymphocytes declines after the stress, whereas the neutrophil number continues to increase. When exercise is performed during hypoxia, the exercise-induced immune changes are pronounced. There is some evidence that the exercise- and hypoxia-induced changes in leukocyte subpopulations are mediated by neuroendocrinological factors such as catecholamines, growth hormone, and cortisol. In contrast, although exercise, as well as hypoxia, is associated with increased plasma levels of IL-6, the mechanisms are not likely to be the same. Thus, during exercise, contracting skeletal muscles are the main source of IL-6 production, whereas the source of IL-6 during hypoxia has not been demonstrated. The increased level of adrenaline contributes to the enormous increase in plasma IL-6 only to a minor degree during strenuous exercise. However, the only modest increase in IL-6 during hypoxia may be linked to hormonal changes, whereas the prolonged increase in IL-6 during chronic hypoxia is likely to be multifactorial.

Exercise and the immune system: regulation, integration, and adaptation

Stress-induced immunological reactions to exercise have stimulated much research into stress immunology and neuroimmunology. It is suggested that exercise can be employed as a model of temporary immunosuppression that occurs after severe physical stress. The exercise-stress model can be easily manipulated experimentally and allows for the study of interactions between the nervous, the endocrine, and the immune systems. This review focuses on mechanisms underlying exercise-induced immune changes such as neuroendocrinological factors including catecholamines, growth hormone, cortisol, beta-endorphin, and sex steroids. The contribution of a metabolic link between skeletal muscles and the lymphoid system is also reviewed. The mechanisms of exercise-associated muscle damage and the initiation of the inflammatory cytokine cascade are discussed. Given that exercise modulates the immune system in healthy individuals, considerations of the clinical ramifications of exercise in the prevention of diseases for which the immune system has a role is of importance. Accordingly, drawing on the experimental, clinical, and epidemiological literature, we address the interactions between exercise and infectious diseases as well as exercise and neoplasia within the context of both aging and nutrition.

Effects of ATP on phosphoinositide hydrolysis and prostaglandin E2 generation in rabbit astrocytes

Extracellular ATP secreted from stimulated nerves plays a role in neurotransmission. This study examined the effects of extracellular ATP on phospholipase A2 and C signalling pathways in rabbit astrocytes. ATP caused prostaglandin E2 (PGE2) generation and phosphoinositide hydrolysis in a time- and concentration-dependent manner. A P2y purinoceptor-selective agonist, 2-methylthio-ATP also caused phosphoinositide hydrolysis, but not PGE2 generation. A P2x purinoceptor-selective agonist, alpha, beta-methylene-ATP did not cause either phosphoinositide hydrolysis or PGE2 generation. Although pertussis toxin had no effect on 2-methylthio-ATP-induced phosphoinositide hydrolysis, it markedly decreased ATP-induced PGE2 generation, with significant inhibition of phosphoinositide hydrolysis. Dexamethasone and indomethacin which potently inhibited ATP-induced PGE2 generation, caused partial inhibition of phosphoinositide hydrolysis, suggesting that pertussis toxin-sensitive component of ATP-induced phospholipase C activation is mediated by cyclo-oxygenase metabolites of arachidonic acid. These results suggest that a stimulation of P2y receptor results in phospholipase C activation in a pertussis toxin-insensitive manner, and that a P2 receptor other than the P2y or P2x subtypes is involved in ATP-induced phospholipase A2 activation via a pertussis toxin-sensitive G protein.

Effects of nordihydroguaiaretic acid on murine antibody-dependent cellular cytotoxicity

The purpose of this study was to analyze the effects of nordihydroguaiaretic acid, an inhibitor of the lipoxygenase pathway of arachidonic acid, on antibody-dependent cellular cytotoxicity. Antibody-dependent cellular cytotoxicity mediated by murine spleen cells was significantly inhibited by concentrations of nordihydroguaiaretic acid from 10(-5) to 10(-4) M (1C50 = 2 x 10(-5) M). The inhibitory effect of nordihydroguaiaretic acid was also observed on antibody-dependent cellular cytotoxicity mediated by macrophage-depleted spleen cells as well as isolated macrophages. Nordihydroguaiaretic acid was highly effective when added at the beginning of the assay and was always present throughout the assay, but failed to inhibit the binding of effector and target cells. The inhibition produced by nordihydroguaiaretic acid could not be reversed by leukotriene B4, a 5-lipoxygenase product. These results suggest that arachidonic acid metabolites other than leukotriene B4 are released by different populations of spleen cells to positively regulate important events in the postbinding phase of murine antibody-dependent cellular cytotoxicity.

Inhibition by 5'-methylthioadenosine of cell growth and tyrosine kinase activity stimulated by fibroblast growth factor receptor in human gliomas

Stimulation of three human glioma cell lines with basic fibroblast growth factor (bFGF) led to the enhancement of cell growth and the rapid tyrosine phosphorylation of cellular proteins, including major substrates of 90 kD. A methyltransferase inhibitor, 5'-methylthioadenosine (MTA), inhibited dose dependently the bFGF-stimulated cell growth and protein tyrosine phosphorylation in glioma cells by blocking both receptor autophosphorylation and substrate phosphorylation, as shown by immunoblotting with antiphosphotyrosine antibodies and cross-linking bFGF to receptors. The antiproliferative activity of MTA correlated quantitatively with its potency as an inhibitor of bFGF-stimulated protein tyrosine kinase activity. The methyltransferase inhibitor MTA had no effect on either epidermal growth factor- or platelet-derived growth factor-stimulated protein tyrosine phosphorylation in glioma cells, but inhibited specifically bFGF-stimulated protein tyrosine kinase activity. The concentration of MTA required for inhibition of protein methylation correlated well with the concentration required for inhibition of bFGF-stimulated cell growth and protein tyrosine phosphorylation. Because MTA had no effect on numbers and dissociation constants of high- and low-affinity bFGF receptors, the inhibition of bFGF-stimulated bFGF receptor tyrosine kinase activity is not likely to be the result of a reduction in bFGF receptor and bFGF binding capacity. In fact, MTA delayed and reduced the internalization and nuclear translocation of bFGF, and the internalized bFGF was submitted to a limited proteolysis that converted it to lower molecular peptides whose presence remained for at least 22 hours. The effect of MTA on bFGF-stimulated tyrosine phosphorylation was immediate and readily reversible.

A requirement for membrane-associated phospholipase A2 in platelet cytotoxicity activated by receptors for immunoglobulin G and complement

Platelets are potent antibody- and complement-dependent cytotoxic effector cells. We showed previously that a single platelet can lyse a target cell sensitized with immunoglobulin G (IgG) and complement components up to C3 (C integral of 3b denotes the target cell-bound fragment of complement up to C3; the precise nature of the bound C3 fragment has not been established), and that the complete cytotoxic system capable of specific recognition and lysis resides in platelet membranes. To define the components of platelet membranes required for cytotoxicity, a set of inhibitors of phospholipase A2 (PLA2) that act by different chemical mechanisms was tested. The lytic reaction is blocked at appropriate concentrations of bromophenacylbromide, mepacrine, and manoalide. When platelets are treated with bromophenacylbromide, inhibition of cytolytic activity and that of PLA2 enzymatic activity occur in parallel. Platelets release arachidonate when incubated with target cells bearing IgG and C integral of 3b, confirming that Fc gamma R and complement receptor trigger both PLA2 action and efficient lysis. Inhibition by thimerosal of a reverse reaction, i.e., reacylation catalyzed by acyltransferase, causes increased target cell lysis, presumably by increasing the products of PLA2 action. Platelet cytotoxicity is increased when platelets are pretreated with some products of PLA2: exogenous lysophospholipids and not free arachidonic acid increase cytotoxicity. Electron microscopy suggests that platelets and target cells may fuse, possibly as a result of the formation of lysophospholipids which are well-known membrane fusogens. Fixation with paraformaldehyde does not affect platelet cytotoxicity, suggesting that the complete cytotoxic system resides as a preformed complex in platelet membranes. The results indicate that platelet membrane-associated PLA2, together with receptors for Fc and complement, are required for platelet cytotoxicity.

Effects of lipoxygenase and cyclooxygenase inhibitors on murine antibody-dependent cellular cytotoxicity (ADCC)

The purpose of this study was to determine the effects that specific inhibition of arachidonic acid (AA) metabolism has on the antibody-dependent cellular cytotoxicity (ADCC) of murine spleen cells. The action of three inhibitors of the lipoxygenase (LO) pathway--nordihydroguaiaretic acid (NDGA), esculetin (Es), and phenanthroline (Phe)--was compared with that of three inhibitors of the cyclooxygenase (CO) pathway--indomethacin (INDO), acetyl salicylic acid (ASA), and imidazole (IMI). All the LO inhibitors suppressed ADCC function in a dose-dependent manner, but NDGA was the most potent inhibitor of this cytolytic activity. In fact, NDGA inhibited the ADCC function with 97% inhibition at 100 microM, while Phe and Es, at the same concentration, inhibited ADCC by 21% and 19%, respectively. However, CO inhibitors did not markedly affect ADCC function and only some doses of them had a slight, but significant, depressing effect (8-11% inhibition at 0.01-0.1 microM of INDO, 7% inhibition at 400 microM of ASA, and 13% inhibition at 800-1000 microM of IMI). These results suggest the LO pathway of the arachidonic acid metabolism plays an important role in regulating ADCC activity of murine spleen cells and the products of the CO pathway have little effect on ADCC lysis.

Effects of in vivo hyperthermia on natural killer cell activity, in vitro proliferative responses and blood mononuclear cell subpopulations

This work was designed to test the hypothesis that elevations in body temperature of humans induce immunostimulation. Eight healthy volunteers were immersed in a water bath (water temperature 39.5 degrees C) for 2 h, during which their rectal temperature rose to 39.5 degrees C. On a later day they served as their own controls, being immersed into thermoneutral water (34.5 degrees C) for 2 h. Blood samples were collected before immersion, at body temperatures of 38 degree C, 39 degree C and 39.5 degree C, and 2 h after water immersion. The interleukin-2 (IL-2) enhanced natural killer (NK) cell activity (lysis per fixed number of mononuclear cells), as well as the proportion and total number of NK cells (CD16+ cells), increased significantly during hyperthermia compared with control values. The lymphocyte proliferative responses did not differ significantly between hyperthermia and thermoneutral conditions. The proportion of pan-T (CD3+) cells was maximally depressed 2 h after water immersion. The decreased proportion of CD3+ cells was mainly due to a decreased percentage of CD4+ cells (not significant). The proportion of B cells (CD19+ cells) did not fluctuate significantly, while a marked and significant increase in monocyte proportion (CD14+ cells) was found 2 h after hyperthermia. Two hours after hot water immersion the lymphocyte concentration declined while the neutrophil and monocyte concentrations were augmented. Induced hyperthermia causes significantly increased serum cortisol, plasma norepinephrine and plasma epinephrine concentrations compared to controls. It is possible that the altered immune functions induced by elevated body temperature can be ascribed to altered composition and function of blood mononuclear cells induced by elevated levels of stress hormones.

Immunoregulatory effects of phospholipase A2 (PLA2) on the proliferation of human lymphocytes

Extracellular phospholipase A2 (PLA2) is a proinflammatory enzyme found especially in the inflammatory exudate to modulate blood flow to areas of antigen stimulation. In this study we found that PLA2 exerted a biphasic effect on the proliferation of phytohemagglutinin (PHA)-stimulated human mononuclear cells (PHA MNC). At low concentrations range from 0.001 to 1 U/ml, PLA2 enhanced the proliferation of PHA MNC (maximal increase was 37.0 +/- 5.67%). Conversely, at concentrations over 10 U/ml, PLA2 markedly suppressed the PHA-induced MNC proliferation (maximal decrease was 88.86 +/- 2.89%). PLA2 was non-toxic to lymphocytes after three days culture, unless the concentration was higher than 100 U/ml. The membrane polarization of PHA-stimulated lymphocytes was also increased by PLA2 at a low concentration. In addition, PLA2 displayed a similar effect on the proliferation of streptokinase-streptodornase (SK/SD) or allogeneic cell stimulated lymphocytes. The change of lymphocyte proliferation by PLA2, was parallel to the change of percentage of helper T cells. Furthermore--a CD4-rich population was proved more susceptible to PLA2 effect than a CD8-rich population. Para-bromophenacyl bromide (pBPB), an irreversible inhibitor of PLA2, abrogated the biphasic effect of PLA2 on PHA MNC proliferation. These results suggest that PLA2 plays a regulatory role on immune reactions by modulating the percentage of helper T cells.

The effects of dexamethasone, betamethasone, flunixin and phenylbutazone on bovine natural-killer-cell cytotoxicity

A series of in-vitro experiments was performed utilizing the ability of bovine peripheral-blood mononuclear cells (PBMC) to induce lysis of Madin-Darby bovine kidney (MDBK) cells infected with bovine herpesvirus 1 (BHV1), in an antibody-independent natural-killer(NK)-cell cytotoxic assay. The effects of dexamethasone (dexamethasone sodium phosphate), betamethasone (betamethasone sodium phosphate), flunixin (flunixin meglumine) and phenylbutazone on this NK cytolysis were studied using concentrations of the drugs ranging from well below to well above those normally attained in plasma at recommended therapeutic doses. All four drugs inhibited NK activity. For each agent a minimum inhibitory concentration (MIC50) required to inhibit NK activity by approximately 50% was calculated. For dexamethasone, betamethasone and flunixin the MIC50 was lower after a 24-h pre-incubation of PBMC with each drug, although a marked inhibition was seen when the drug was only present during the 5-h NK assay itself. In contrast the MIC50 for phenylbutazone rose after a 24-h pre-incubation with PBMC.

The effect of the platelet-activating factor antagonist, BN 52021, on human natural killer cell-mediated cytotoxicity

The influence of the platelet-activating factor (PAF) antagonist, BN 52021, on human natural killer (NK) cell cytotoxicity against K 562 target cells was determined. Cytotoxicity was measured by a short-term (4 hr) 51Cr-release assay. The cytotoxicity was significantly reduced in the presence of PAF antagonist at concentrations from 30 to 120 microM. This reduction of killing was not due to the impairment of binding of effector cells to target cells. Pretreatment of K 562 target cells with the PAF antagonist led to a greater inhibition of NK cell cytotoxicity compared with that observed when the effector cells were preincubated with BN 52021. Thus, the inhibition of cytotoxicity appears to be due to an effect of BN 52021 on target cells rather than on lymphocytes. Furthermore, the increase in NK activity induced by interferon was less pronounced when BN 52021 was added in the incubation medium. The natural cytotoxicity of platelet-depleted or large granular lymphocyte-enriched effector cell populations was inhibited by the PAF antagonist in a similar manner. The effect of BN 52021 appears to be related to its specific PAF antagonistic activity since a similar action on NK cells was noted with two other structurally unrelated PAF antagonists, BN 52111 and WEB 2086. In contrast, Ginkgolide J (BN 52024), which is structurally related to BN 52021 but lacks PAF antagonistic activity, was ineffective in inhibiting NK cell cytotoxicity. Finally, synthetic PAF induces a dose-dependent cytotoxic action on K 562 cells and this effect of the autacoid is inhibited by BN 52021. These observations provide indirect evidence that PAF could play a role in the mechanism(s) of NK cytotoxity.

Plasma from uninephrectomized rats stimulates phospholipid methylation and arachidonic acid release in renal-cortical slices

Phospholipid methylation and arachidonic acid release in renal-cortical slices was investigated in vitro after addition of plasma from uninephrectomized or sham-operated rats. Plasma from uninephrectomized rats ('uni-plasma') stimulated phospholipid methylation when obtained within the first 3 h after uninephrectomy. With different amounts of added plasma a graded response in phospholipid methylation was obtained. Addition of 50 nM-12-O-tetradecanoylphorbol 13-acetate for 10 min to intact slices also stimulated phospholipid methylation, whereas incubation of slices before addition of 'uni-plasma' with 100 microM-1-(5-isoquinolinylsulphonyl)-2-methylpiperazine prevented it, suggesting that protein kinase C stimulates phospholipid methylation in renal-cortical slices. Plasma from uninephrectomized rats also stimulates [3H]arachidonic acid release from phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) via activation of phospholipase A2. Two mechanisms of phospholipase A2 activation are proposed: first, in which it is activated by protein kinase C and releases 3H radioactivity from PtdCho, and second, in which phospholipase A2 is stimulated by Ca2+ ions and releases 3H radioactivity from PtdEtn.

Biology of natural killer cells

Studies of cytotoxicity by human lymphocytes revealed not only that both allogeneic and syngeneic tumor cells were lysed in a non-MHC-restricted fashion, but also that lymphocytes from normal donors were often cytotoxic. Lymphocytes from any healthy donor, as well as peripheral blood and spleen lymphocytes from several experimental animals, in the absence of known or deliberate sensitization, were found to be spontaneously cytotoxic in vitro for some normal fresh cells, most cultured cell lines, immature hematopoietic cells, and tumor cells. This type of nonadaptive, non-MHC-restricted cellmediated cytotoxicity was defined as “natural” cytotoxicity, and the effector cells mediating natural cytotoxicity were functionally defined as natural killer (NK) cells. The existence of NK cells has prompted a reinterpretation of both the studies of specific cytotoxicity against spontaneous human tumors and the theory of immune surveillance, at least in its most restrictive interpretation. Unlike cytotoxic T cells, NK cells cannot be demonstrated to have clonally distributed specificity, restriction for MHC products at the target cell surface, or immunological memory. NK cells cannot yet be formally assigned to a single lineage based on the definitive identification of a stem cell, a distinct anatomical location of maturation, or unique genotypic rearrangements.

Involvement of a serine protease in tumour-necrosis-factor-mediated cytotoxicity

We investigated the effect of various protease inhibitors on the anti-proliferative and cytotoxic action of tumour necrosis factor (TNF) on mouse L929 fibrosarcoma cells. 1. The following serine-type protease inhibitors led to inhibition of TNF action: phenylmethylsulfonyl fluoride, N alpha-p-tosyl-L-lysine chloromethane, N alpha-p-tosyl-L-phenylalanyl chloromethane, N alpha-p-tosyl-L-arginine methyl ester, L-leucine methyl ester, DL-phenylalanine methyl ester, N-acetyl-DL-phenylalanine-beta-naphthyl ester, p-nitrophenyl p'-guanidino-benzoate and antipain. We could not detect an effect of inhibitors specific for thiol protease on TNF. 2. Inhibition of TNF-mediated cytotoxicity was evident in both the presence and absence of actinomycin D or cycloheximide. 3. TNF itself was not found to be a protease, as it had no proteolytic activity in a sensitive colorimetric assay. [1,3-3H]Diisopropyl fluorophosphate, an effective irreversible inhibitor of serine proteases, did not bind to TNF. Pretreatment of TNF with N alpha-p-tosyl-L-lysine chloromethane did not influence its biological activity. 4. The addition of protease inhibitor to the cells at various times after TNF administration led to a gradual loss of protection, suggesting that the protease acts at a rather late stage. 5. Protease inhibitors did not influence TNF binding, internalization or metabolization. 6. No increase in supernatant protease activity or in cell-associated protease activity could be detected after treatment of L929 cells with TNF. Our results document the involvement of protease activity, acting quite late during the cytolytic and growth inhibiting processes induced by TNF.

Density and localization of lymphocytes with natural-killer (NK) cell activity in periodontal biopsy specimens from patients with severe periodontitis

Natural killer lymphocytes (NKL) in gingival biopsy specimens of 13 patients with advanced periodontitis and 6 normal control subjects have been evaluated by the monoclonal antibody NC 1, anti-B4 and a double immunoenzymatic labeling technique, combining the peroxidase-anti-peroxidase (PAP) method with the alkaline-phosphatase-anti-alkaline-phosphatase (APAAP) technique. Mononuclear cells with NK-activity (NKA) were mainly accumulated in the upper to middle third of the periodontal pocket. The concentration of NC-1-positive cells (CNC) of the baseline biopsy specimens was significantly increased at p = 0.05 compared to the CNC after hygiene training. The statistical difference rose to p = 0.01 following scaling, root planing and curettage therapy. The healthy gingiva of control subjects showed an average of 1-2 NKL, and no statistical difference could be found when compared to the CNC of the biopsy specimens of patients after periodontal therapy. These data support the hypothesis that antibody-dependent cytotoxic immunoreactive lymphocytes in chronic inflammatory periodontal disease can be reduced by scaling and root planing therapy.

Modulation of natural killer cell activity in peripheral blood by physical exercise

The present study was designed to examine the effect of physical exercise on human natural killer (NK) cells. Six healthy volunteers underwent two different acute physical exercise tests with an interval of at least 1 week: (1) 60 min bicycle exercise at 80% of maximal oxygen uptake (VO2max) and (2) 60 min back-muscle training at up to 29% of VO2max; blood samples were collected before and during the last few minutes of exercise, as well as 2 h and 24 h afterwards. The NK cell activity (lysis/fixed number of mononuclear cells) increased during bicycle exercise, dropped to a minimum 2 h later and returned to pre-exercise levels within 24 h. Back-muscle exercise did not significantly influence NK cell activity. Plasma levels of adrenaline, noradrenaline, and cortisol were elevated during bicycling, but not during back-muscle exercise, indicating that exercise intensity is a determinant of NK cell activity. During bicycle exercise the NK cell subset (CD16- cells) of mononuclear cells increased significantly. Furthermore an improved interleukin 2 (IL-2) boosting of the NK cell activity was found during work as compared to IFN-alpha and indomethacin-enhanced NK cell activity. These results indicate that NK cells with a high IL-2 response capacity are recruited to the peripheral blood during exercise. The decreased NK cell activity demonstrated 2 h after work was probably not due to fluctuations in size of the NK cell pool, since the proportion of CD16+ cells was normal. The finding that indomethacin fully restored the suppressed NK cell activity in vitro and the demonstration of a twofold increase in monocyte (CD20+ cells) proportions 2 h after work, strongly indicate that prostaglandins released by monocytes during the heavy physical exercise are responsible for the down-regulation of the NK cells.

Perforin-dependent and -independent pathways of cytotoxicity mediated by lymphocytes

There is little doubt at the present time that both perforin-dependent and -independent pathways are important in mediating the cytotoxicity associated with lymphocytes. The cell distribution of perforin, initially thought to include both CTL and NK cells, now must be viewed with caution because all previous biochemical studies on CTL have been conducted with cell lines propagated in long-term cultures in the presence of T cell growth factors (IL-2 and perhaps some still undefined factors). Under these conditions, CTL are known to assume a broader, NK-like specificity in target cell killing and may thus differ significantly from primary CTL generated in the body. Accordingly, perforin does not seem to be present in primary CTL activated directly through mixed lymphocyte reactions. It remains to be shown how primary CTL lyse target cells in vivo. Initial studies conducted in several laboratories have already provided some clues. It now seems that even in cultured, perforin-containing CTL, the perforin pathway is not an obligatory mechanism required for target cell killing. Other pathways, possibly involving TNF/lymphotoxin-like molecules, may play a direct role in this type of cytotoxicity. Other still unidentified factors now also need to be sought, including membrane polypeptides that may develop cytotoxicity directly upon cell contact and binding. Although from the studies reviewed here it is clear now that perforin has a more limited role in cell killing than originally proposed, it is still intriguing that it should share structural and functional homologies with complement proteins, drawing paradoxical analogies between two systems (the cellular and the humoral immune systems) which have evolved to become specialized to carry out separate immunological tasks. The cloning of the genes for perforin and for all the C proteins that comprise the MAC should reveal important information on how these genes originated and then diverged during evolution. The cellular distribution of other granule products, such as serine esterases, also must be viewed with caution. A serine esterase activity was initially thought to be CTL-specific. This information stimulated an intensive research activity in many laboratories that resulted in both the purification of a serine esterase family and the cloning of several serine esterase transcripts. It is becoming clear from recent evidence that this group of enzymes is not truly CTL-specific and therefore would not be expected to develop any function rendered absolutely necessary for cytolysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Depressed natural killer cell activity in acute myocardial infarction

Natural killer (NK) cell activity against K562 target cells was measured in patients within 24 h of acute myocardial infarction (AMI) and regularly thereafter for 6 weeks. NK cell activity was suppressed on days 1, 3, and 7 (P less than 0.01), day 14 (P less than 0.05) and at 6 weeks (P = 0.05) when compared to controls. Interferon, interleukin 2 and indomethacin enhanced NK cell activity on all days measured, but did not completely restore the defective NK cell activity. Serum from the patients did not suppress the NK cell activity of healthy mononuclear cells. The number of NK cells, identified as large granular lymphocytes (LGL), measured on days 1, 3, and 14 and at 6 weeks was not reduced in comparison to that of controls. Thus, the defective NK cell activity can be characterized as functional.

Interferon alpha/beta induces changes in the metabolism of polyenoic phospholipids and diacylglycerols in the livers of suckling mice

Suckling mice were injected daily from birth for 10 days with potent preparations of mouse interferon alpha/beta. Interferon treatment resulted in a markedly lower concentration of polyunsaturated fatty acids (20:4 omega 6 and 22:6 omega 3) in the two principal liver phospholipids, phosphatidylcholine and phosphatidylethanolamine, than in livers of control-treated mice. This effect appeared to correlate with a low level of synthesis of polyunsaturated phospholipids in the livers of interferon-treated mice. Thus, in control mice, synthesis of species of polyunsaturated phospholipids increased markedly in the first 10 days of life, whereas in 10-day-old interferon-treated mice, the level of synthesis of species of polyunsaturated phospholipids was comparable to that in newborn mice. In parallel, a marked increase in the diacylglycerol content without change of its renewal was observed in the livers of interferon-treated mice. We suggest that interferon treatment results in an inhibition of one of the processes that leads to activation of the enzymatic systems responsible for the synthesis of species of polyunsaturated phosphatidylcholine and phosphatidylethanolamine in the liver of suckling mice. It seems likely that these results are related to the inhibition of liver cell maturation and the marked cell necrosis that are observed in interferon-treated suckling mice.

In vitro natural killer activity against progressive and regressive variants of a rat colon adenocarcinoma. Effect of treatments with anti-asialo GM1 plus complement

In a previous work, a cell line (DHD/K12) was established from a colon adenocarcinoma induced in a BDIX rat by 1,2-dimethylhydrazine. From this line, two cloned sublines, PROb and REGb, were then isolated. When subcutaneously inoculated into syngeneic rats, PROb cells yield progressive tumors, whereas REGb cells yield tumors which regress. In this study, in a 16-h 51Cr release assay, natural cytotoxicity mediated by BDIX splenic nonadherent lymphoid cells (NK cells) was shown to be much higher against REGb cells than against PROb cells. Whatever the target cells, NK cytotoxicity was always higher when the effector cells were obtained from males rather than from females. Treatment of BDIX splenic lymphocytes by anti-asGM1 serum plus complement revealed that both anti-asGM1 sensitive and non-sensitive NK cells exist. The activity of anti-asGM1 non-sensitive NK cells appeared to be minor and to be detected only when the level of cytotoxicity before treatment was sufficiently high. The difference between PROb and REGb tumor growth appears to be linked, at least in part, to a higher sensitivity of REGb cells to NK cells and especially to anti-asGM1-sensitive NK cells.

Development of phospholipase A2 and lysophosphatidylcholine metabolising enzyme activities in the neonatal rat intestine

We have studied the development of phospholipase A2 (PLA2) and lysophosphatidylcholine (lysoPC)-metabolising enzyme activities in the neonatal rat intestine and its relation to the intestinal permeability of macromolecules. The permeability was determined by feeding young rats a mixture of bovine serum albumin, bovine immunoglobulin G and fluorescein-isothiocyanate-conjugated dextran 70,000, and analysing the serum concentrations after six hours. The animals were then killed and the intestinal mucosa was homogenised and assessed for PLA2 and lysoPC-metabolising enzyme activities. The intestine was 'open' to the macromolecules in 14 day old animals, but 'closed' in 22 and 32 day old animals and in 14 day old rats treated with cortisone acetate on day 10, 11, and 12 postpartum. The activity of PLA2 (at pH 6 and 2 mM Ca2+) was higher in 32, 22, and cortisone treated 14 day old animals, than in untreated, 14 day old animals. Incubation of 14C-acyl-lysoPC with mucosa from 14 day old rats did not change the radioactivity pattern as shown by thin layer chromatography, whereas after incubation with mucosa from 22 or 32 day old animals all the radiolabel was found in free 14C-fatty acid and in 14C-phosphatidylcholine. These findings indicate that mucosal PLA2 activity increases during intestinal maturation and that the mucosa acquires the ability to acylate and deacylate lysoPC when it is 'closed' to macromolecules.

Cell-mediated cytotoxicity by natural killer and killer cells, lipid peroxidation and glutathione

In the course of spontaneous cell-mediated cytotoxicity (SCMC) and antibody-dependent cell-mediated cytotoxicity (ADCC) with human peripheral lymphocytes as effector cells, no lipid peroxidation occurred as measured by the production of ethane and thiobarbituric acid-reactive material. Furthermore, impairment of major cellular defense systems of target cells (K562 cells for SCMC, Chang liver cells for ADCC), by decreasing their glutathione content, had no effect on either lipid peroxidation or the cytotoxic response. These findings indicate that peroxidative damage is not a mechanism of NK and K cell-mediated cytotoxicity.

Reversible inhibition of lymphokine-activated killer cell activity by lipoxygenase-pathway inhibitors

Natural killer (NK) cells and lymphokine-activated killer (LAK) cells are anomalous cytotoxic cells which are potentially important in host defense against cancer. Several studies have demonstrated that natural killer (NK) cell activity can be suppressed by chemical inhibitors of the lipoxygenase pathway through inhibition of the production of leukotriene B4 (LTB4). The present study investigated the effects of the lipoxygenase inhibitors BW755C and nordihydroguaiaretic acid (NDGA) on NK and LAK cell activity. NK cell function of fresh peripheral blood mononuclear cells (PBMC) was determined via a standard chromium release assay employing K562 as the tumor target. The LAK cell activity of PBMC which had been stimulated with 10 IU of interleukin-2 for 72 hr was determined against the NK-resistant cell line Daudi. Both BW755C and NDGA inhibited NK and LAK cell function at a variety of concentrations. Indomethacin, a prostaglandin synthesis inhibitor, did not bring about an appreciable diminution in NK or LAK cell activity. Inhibition of NK and LAK cell activities by BW755C and NDGA could be reversed by washing the effector cell suspensions prior to the cytotoxic assay or by adding LTB4 (10(-11)-10(-8) M) directly to the effector:target suspensions. These data indicate that certain arachidonic acid oxidation products of the lipoxygenase pathway are essential for the function of LAK cells.

Regulation of human natural killing. IV. Role of lipoxygenase in regulation of natural killing activity

In this study we demonstrated that natural killer (NK) cell lysis by human peripheral blood nonadherent (NA) cells against K562 target cells was rapidly inhibited by four agents that inhibit the lipoxygenase pathway of arachidonic acid metabolism, nordihydroguaiaretic acid (NDGA), U-60257, alpha-phenanthroline, and esculetin. However, human NK cells activated by interferons (IFN) or poly I:C were partially resistant to suppression by NDGA and U-60257. Pretreatment of the NA cells with the four lipoxygenase inhibitors at 37 degrees C for 18 h led to suppression of NK activity. The inhibition of NK activity by NDGA was not reversed by aspirin at a concentration that inhibits PGE2 synthesis. Thus, suppression of NK activity by NDGA was not mediated by the effects on PGE2 synthesis. However, the inhibition of endogenous NK activity by NDGA, U-60257, alpha-phenanthroline, or esculetin was partially reversed by IFN or poly I:C. These results suggest that products of lipoxygenation are required for maintenance of human NK activity.

Characterization of the in vitro effects of glucocorticosteroids on NK cell activity

The NK cell activity of mononuclear cells as well as monocyte-depleted, Percoll-fractionated, NK cell-enriched effector cells against K 562 target cells was inhibited by methylprednisolone (MP) and hydrocortisone (HC) in a dose-dependent manner. The effector/target cell conjugate formation was studied in a single cell agarose assay, and it was shown that MP and HC partly inhibited the NK cell activity by inhibition of the adhesion of effector cells to target.

Two natural killer-cell subpopulations distinguished by heat sensitivity

We examined the effect of heat on natural killer-cell activity and found that two different natural killer-cell subpopulations can be distinguished by their heat sensitivity; one subpopulation loses natural killer-cell activity at 41 degrees C, and the other is not affected. In a single-cell assay, the ability of natural killer cells to conjugate to K 562 cells was not affected by incubation at 41 degrees C, but the killer activity of natural killer cells after conjugating to K 562 cells was reduced at 41 degrees C. Therefore it is likely that the difference in heat sensitivity between the two subpopulations is due to postbinding cytolytic events. Tetracaine, which influences cytolytic events, was used to examine whether or not the two natural killer-cell subpopulations can be distinguished by tetracaine sensitivity. However, it was found that tetracaine inhibits natural killer-cell activity equally for both of these natural killer-cell subpopulations.

The mechanism of the inhibitory effect of progesterone on lymphocyte cytotoxicity: I. Progesterone-treated lymphocytes release a substance inhibiting cytotoxicity and prostaglandin synthesis

Progesterone-treated lymphocytes (generator lymphocytes) of healthy pregnant women release a nondialyzable factor that inhibits both cytotoxic activity and prostaglandin F2 alpha synthesis of test lymphocytes. Production of this factor is blocked by protein synthesis inhibitors (cycloheximide and actinomycin D). Sodium dodecylsulfate polyacrylamide electrophoresis of the partially purified material revealed a main 34,000 MW protein band. Progesterone-treated lymphocytes of pregnant women showing clinical symptoms of threatened preterm delivery (risk group) failed to release this substance.

The effect of acute exercise on natural killer-cell activity of trained and sedentary human subjects

The effect of acute exercise on natural killer (NK) activity and on the distribution of phenotypic characteristics of peripheral blood lymphocytes was examined. Trained and sedentary individuals underwent a standard progressive exercise test on a cycle ergometer using an incremental work load of 15 W (90 kpm), increased every minute. Each subject was encouraged to exercise to exhaustion, and total ventilation and mixed expired O2 and CO2 were measured every 30 sec. All subjects reached the "anaerobic" threshold as judged by the deflection of ventilation at a work load near VO2max. NK activity against K562 reached maximum levels immediately after exercise, dropped to a low point 120 min later, then slowly came back to preexercise levels within 20 hr. No significant differences were observed between the trained and the sedentary groups. Furthermore, immediately after exercise the proportion of OKT-3+ and OKT-4+ cells was reduced by 29.8 +/- 3.6 and 33.6 +/- 5.4%, respectively; the percentage Leu-7+ and Leu-11a+ cells was increased by 53.9 +/- 1.7 and 57.3 +/- 2.9%, respectively. The percentage OKT-8+ cells was not significantly altered. When the percentage binding of effector to target cells was examined, it was highest at 0 min post-exercise (19 +/- 6.2%) and lowest at 120 min postexercise (7 +/- 3.9%), but the absolute number of NK cells remained unchanged. The source of serum used in the lytic assay had no effect on the NK activity, as fetal calf serum and autologous sera drawn at different time intervals during exercise gave similar results.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of human natural killing by lysosomotropic and thiol-reactive agents

Treatment of human peripheral blood lymphocytes (PBL) with ammonium or other lysosomotropic amines eliminates natural killing (NK) activity of effector cells without affecting their viability. Inhibition of NK by these reagents is probably due to blocking of events subsequent to effector cell target cell binding but before programming for cytolysis. Treatment of K562 target cells with the same reagents has no effect on target cell sensitivity to NK. Pretreatment of effector cells with the NK inhibitory lysosomotropic agents decreases lysosomal thiol cathepsin activity without affecting the lysosomal acid phosphatase activity. Thiol-reactive agents, tosyl-L-lysine chloromethyl ketone (TLCK) and iodoacetamide also inhibit NK and thiol cathepsin activity in PBL. These data suggest a role for thiol-containing enzymes in the early stages of NK cytolysis.

3-Deazaadenosine-induced disorganization of macrophage microfilaments

3-Deazaadenosine (c3Ado) has been reported to inhibit a number of cellular functions. These biological effects of c3Ado have generally been attributed to its ability to act as inhibitor and substrate of S-adenosylhomocysteine hydrolase. In this report, it is revealed by fluorescence microscopy that c3Ado caused disorganization of the microfilament system of mouse macrophages at concentrations (greater than or equal to 5 microM) similar to those that inhibited antibody-dependent phagocytosis and zymosan-stimulated H2O2 production by these cells. Inhibition of phagocytosis and perturbation of microfilaments by c3Ado were completely abrogated by washing the macrophages free of this agent and allowing the cells a 30-min recovery period. Furthermore, these effects of c3Ado on phagocytosis and microfilaments appeared to be independent of the increase in S-adenosylhomocysteine and S-3-deazaadenosylhomocysteine that occurred in these macrophages. First, periodate-oxidized adenosine and 3-deaza(+/-)aristeromycin, two other inhibitors of S-adenosylhomocysteine hydrolase that caused greater increases in macrophage S-adenosylhomocysteine than did c3Ado, had no effect on either phagocytosis or microfilaments. Second, pretreatment of macrophages with periodate-oxidized adenosine (to inhibit S-adenosylhomocysteine hydrolase) prevented the subsequent metabolism of c3Ado to S-3-deazaadenosylhomocysteine but did not diminish the effects of c3Ado on phagocytosis or microfilaments. These results demonstrate that c3Ado can perturb the microfilament system of cells and provide an alternative mechanism for the biological effects of c3Ado.

Studies of the phospholipase A2 activity of rat ileal mucosa

A rapid and simple procedure has been used to determine phospholipase A2 activity (EC 3.1.1.4) in rat ileal mucosa. We used 14C-oleate-labeled Escherichia coli as substrate for the phospholipase activity and a 0.45-micron Millipore filter to separate the product of hydrolysis--the 14C-oleic acid--from the unhydrolyzed substrate. The phospholipase A2 activity was optimal at pH 9.8 and at 2 mM Ca2+, but another peak of activity appeared at pH 7.2. In addition, cell fractionation revealed yet another phospholipase A2 activity at pH 5.0 in the absence of Ca2+. These findings suggest the presence of more than one phospholipase A2 in the ileal mucosa and points to the possible use of a simple procedure for studying their distribution and properties.

Effect of 5'-methylthioadenosine, 3-deazaadenosine, and related compounds on human natural killer cell activity. Relation to cyclic AMP and methylation potential

The effect of 5'-methylthioadenosine (MTA) on human natural killer (NK) cell activity was examined and compared with the effect of 3-deazaadenosine (c3-ado) and periodate-oxidized adenosine (ado-ox). MTA inhibited NK cell activity in concentrations above 30 microM, but in concentrations below 10 microM a slight enhancing effect was often observed. C3-ado and ado-ox were 10 and 3 times more potent, respectively, as inhibitory agents and did not increase NK cell activity in low concentrations. The inhibitory effect of c3-ado was unaffected by preincubation of the cells but was enhanced by the addition of L-homocysteine. In concentrations that caused inhibition of NK cell activity all three agents caused a fall in the methylation index (AdoMet/AdoHcy) but no or an inconsistent effect on the level of cyclic AMP. An increase in the level of AdoHcy was observed already after 1 h of incubation but was more pronounced after 4 h of preincubation with the adenosine derivatives. The inhibition of cytotoxicity was mainly on their initiation of lysis, with a smaller effect on target cell binding. Antibody-dependent cellular cytotoxicity and lectin-dependent cellular cytotoxicity appeared to be less sensitive to inhibition by c3-ado. Our results show that several adenosine analogues inhibit NK-cell-mediated cytotoxicity in parallel with a decreased methylation index. The results suggest that a methylation step is critical in lymphocyte-mediated cytotoxicity and that NK cell activity is more sensitive to inhibition of this step than antibody- or lectin-dependent cytoxicity.

Calcium signals and phospholipid methylation in eukaryotic cells

Rat basophil leukaemic (2H3) cells, mast cells and mouse thymocytes respond to stimulation by specific ligands with an increase in the free cytosolic Ca2+ concentration. The time courses of these Ca signals and the biological responses have been compared with changes in phospholipid metabolism. Increased phosphoinositide metabolism coincides with the Ca signals and the responses in each cell system, whereas any increase in phospholipid methylation during the response is less than one molecule per receptor and at least 5-50-fold less than the increases reported previously. Furthermore, no significant changes were detected in the concentration of S-adenosylmethionine, the methyl-group donor in the synthesis of methylated phospholipids. The hypothesis that phospholipid methylation is obligatory for receptor-mediated Ca signals is not supported by these data and requires critical re-evaluation.

Local effects of lysophosphatidylserine in rats

To study the inflammatory properties of lysophosphatidylserine (a phospholipid acting as a histamine releaser), rats were subjected to local treatment with this compound. In the paw a rapid and dose-dependent edematous reaction occurred within 30-60 min (ED50 2.5 micrograms/rat). The effect was dependent on the intact configuration of serine head group since lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidic acid and N-acetimidyl-lysophosphatidylserine were uneffective. Indomethacin produced a weak inhibition but chlorpheniramine and cyproheptadine inhibited 50 and 70%, respectively. Consistently, the histamine stores of the paw were found to be decreased at the end of the lysophosphatidylserine effect. Increase in vascular permeability was observed also after the injection of lysophosphatidylserine into the dorsal skin and pleural cavity although the phospholipid was less effective in these regions. The fluid extravasation in the pleural cavity was 75% prevented by cyproheptadine. Parallel in vitro experiments showed that the effect of lysophosphatidylserine on isolated pleural and peritoneal mast cells is increased when a leukocyte lysate was also added. After centrifugation the activity was retained in the insoluble fraction. It is concluded that lysophosphatidylserine, injected locally, elicits an inflammatory reaction mediated by the components of mast cell granulus. The response may be amplified by the migration of other inflammatory cells into the exudate.