Augmentation of lymphokine-activated killer cell cytotoxicity by monoclonal antibodies against human small cell lung carcinoma

This study examined the lymphokine-activated killer (LAK) cell cytotoxicity on monoclonal antibody (MoAb)-bound tumor cells from the human small cell lung carcinoma cell lines H69 and H128. LAK cells were generated from normal peripheral blood mononuclear cells by incubation with interleukin 2 for 3 or more days. Cells from the LAK culture were cytotoxic to natural killer-sensitive (K562, 84% cytotoxicity) and natural killer-resistant (Daudi, 85%; H69 and H128, 69% and 97%, respectively) cell lines, and to freshly excised human lung (49%) and breast (57%) tumors. LAK cytotoxicity to H69 or H128 cells was significantly augmented by target cell preincubation with the small cell lung carcinoma-reactive MoAbs 1096 (increases of up to 271%) or 5023 (up to 223%). SCLC 5023 or 1096 did not enhance LAK cytotoxicity to Daudi cells of lymphoblastoid origin. Pretreatment of LAK cells with an anti-Fc receptor antibody blocked MoAb augmentation by 1096 or 5023 (but not LAK cytotoxicity), suggesting that LAK-MoAb interaction may be mediated by Fc binding. LAK activity coincided with emergence of a large cell [interleukin 2-stimulated large mononuclear leukocyte (LML)] subset expressing the CD16 and NKH-1 surface determinants. Serial immunophenotyping of the LAK cell culture harvested at Days 3, 5, and 7 indicated that the level of LAK cytotoxicity, with or without MoAb augmentation, correlated with frequency of NKH-1-reactive LMLs. These observations support the hypothesis that LAK cytotoxicity is mediated by a NKH-1-reactive LML subpopulation. Antitumor cytotoxicity may be augmented by tumor-reactive MoAbs through Fc binding to this LML subset.     

Cytotoxic Activity of Various LAK Cells against Autologous Lung Cancer, K-562 and Daudi Cells

Comparative cytotoxic activity and specificity studies of lymphokineactivated killer (LAK) cells from different sources and preparationswere carried out. Cytotoxic studies of lymphocytes from regionallymph nodes (Rn-LAK), peripheral blood (Pb-LAK) and those stimulatedby autologous tumor cells and then activated by recombinantinterleukine 2 (St-LAK) against autologous lung cancer cells,were conducted using the ⁵¹Cr-releasing test. The cytotoxicactivities of these three LAK cells against autologous fibroblasts,allogeneic tumor cells, K-562 and Daudi cells were also compared.A time course experiment disclosed that the cytotoxic activityof Pb-LAK cells against autologous tumor cells reached a maximumon day 3 and declined shortly after the peak while that of Rn-LAKcells gradually increased to a maximum on day 7 and remainedat a high titer for at least two weeks. The cytotoxic activityof Rn-LAK cells was significantly higher than that of Pb-LAKcells in seven out of 10 individual experiemnts and that ofstimulated LAK (St LAK) cells was higher than the cytotoxicactivities of the other LAK cells in eight out of nine experiments.A specificity study showed that Rn-LAK cells possessed a highercytotoxic activi ty against autologous tumor cells and a lowercytotoxic activity against autologous fibroblasts and allogeneictumor cells than Pb-LAK cells. A comparative study of cytotoxicactivities against K-562, Daudi cells and autologous tumor cellsbetween St- and Rn-LAK cells demonstrated that although therewas no difference in natural killer activity, cytotoxic activityagainst autologous tumor cells as well as the LAK activity ofSt-LAK cells were higher than that of Rn-LAK cells. These resultsindicate that the activities and specificities of LAK cellsdiffer according to their source and preparation.     

以SMMC—7721为靶细胞MTT法检测LAK细胞活性方法的建立

目的建立以贴壁生长的癌细胞为靶细胞、MTT法检测LAK细胞活性的方法。方法用MTT比色法测定LAK细胞对体外培养的K562、Raji、SMMC－7721细胞的杀伤活性。结果LAK细胞对已知的NK敏感细胞K562及NK耐受细胞Raji均有明显杀伤作用,贴壁生长的SMMC-7721肝癌细胞对NK细胞不敏感,而对LAK细胞敏感,在效靶比为40：1时,LAK细胞对肝癌细胞的杀伤率达90％以上,其杀伤效应随效靶比增高而增高。结论SMMC-7721细胞可作为检测LAK细胞活性的靶细胞。以贴壁细胞作为靶细胞的MTT法检测LAK细胞活性较传统的悬浮细胞如Raji作为靶细胞具有灵敏、准确、简单、可靠的优点,更适用于国内一般实验室开展。     

Synergistic action of a plant rhamnogalacturonan enhancing antitumor cytotoxicity of human natural killer and lymphokine-activated killer cells: chemical specificity of target cell recognition.

The spontaneous natural killer (NK) and lymphokine-activated killer (LAK) cytotoxicity of highly purified CD56+CD3- NK cells (90 to 95%) against NK-sensitive and NK-insensitive target cells was drastically enhanced when a rhamnogalacturonan contained in a commercially available Viscum album extract was present during 4-h cytotoxicity assays. This enhancement correlated strictly with an increased formation of NK cell or LAK cell/tumor cell conjugate formation. Information on the chemical specificity of NK cell and LAK cell interaction with target cells and with the rhamnogalacturonan was obtained from inhibition studies. The most efficient inhibitors (100% inhibition at 5 mg/ml) were acetylated D-mannose and acetylated L-mannonic acid gamma-lactone. They specifically inhibited in a dose-dependent manner: (a) the cytotoxicity of NK cells against K562 cells and the formation of NK cell/K562 cell conjugates; (b) the cytotoxicity of LAK cells against K562 cells and Daudi cells as well as the formation of LAK cell/K562 cell and of LAK cell/Daudi cell conjugates; and (c) the synergistic effects of the rhamnogalacturonan in the cytotoxicity assays and the target cell-conjugate formation assays with NK cells and LAK cells. The inhibitory effects observed after pretreatment of NK cells or LAK cells with acetylated mannose were completely reversible, but that obtained with acetylated mannonic acid gamma-lactone was only partly reversible, and the degree of reversibility depended on the inhibitor concentration applied during pretreatment. Nonacetylated mannose or mannose derivatives up to concentrations of 20 mmol showed no inhibitory effects. A mechanistic model representing the interaction of NK cells and LAK cells with target cells and with rhamnogalacturonan is proposed.     

Inhibition by fibrin coagulation of lung cancer cell destruction by human interleukin-2-activated killer cells.

We examined the effect of fibrin coagulation on tumor cytotoxicity mediated by human lymphokine (IL-2)-activated killer (LAK) cells. LAK cells were induced from peripheral blood mononuclear cells (MNC) by culture with recombinant IL-2 for 4 or 5 days, and LAK cell-mediated cytotoxicity against tumor cells was assessed by 51Cr release assay in the presence or absence of plasma from normal subjects and lung cancer patients. Plasma did not affect the phase of induction of LAK activity by IL-2, but dose-dependently inhibited the effector phase of LAK cell-mediated cytotoxicity against Daudi cells. Similar inhibition of LAK cell-mediated cytotoxicity was observed on pretreatment of Daudi cells and human lung cancer cell lines with human fibrinogen plus thrombin. A parallel relationship was found between the amount of fibrinogen in plasma of lung cancer patients and inhibition of LAK cytotoxicity. This inhibition was reduced by addition of anticoagulants (heparin or argatroban). These findings suggest that fibrin coagulation on tumor cells protects them from LAK cell-mediated tumor cytotoxicity in malignant lesions and that a combination of an anticoagulant drug and IL-2/LAK therapy may be effective for treatment of lung cancer patients.     

Release of esterase from murine lymphokine-activated killer cells in antibody-dependent cellular cytotoxic reaction

Release of granule enzyme(s) (BLT esterase) in the antibody dependent lymphokine-activated killer (LAK) cell-mediated cytotoxic reaction (LAK ADCC) was studied using LAK cells induced from murine splenocytes and thymocytes, various human tumor cells and relevant monoclonal antibodies (mAbs) to the tumor cells. BLT esterase was not significantly released from LAK cells in direct LAK cell-mediated cytotoxic reactions (LAK CMC). However, cultures of LAK cells and IgG-coated target tumor cells resulted in release of the enzyme concomitantly with target cell lysis, although esterase release proceeded faster than target cell lysis. Anti-LFA-1 mAb showed an inhibitory effect on LAK CMC but not on either LAK ADCC or BLT esterase release in the ADCC. These results indicate that exocytosis of granule enzyme from LAK cells is triggered by stimulation of Fc receptor on LAK cells and that LAK CMC and LAK ADCC differ in their lytic mechanism in terms of the release of BLT esterase.     

人LAK细胞的诱导及其生物特性的研究

LAK cell activity of peripheral blood from normal donors was induced by interleukin 2 (IL-2). Optimal induction of LAK cells was obtained by 3-4 day incubation of PBMC in the presence of 30-40 units/ml of IL-2. Several cell lines Raji, CEM, HeLa, 109 (esophageal carcinoma) and OC (ovarian carcinoma) which were NK cell resistant tumor cells could be lysed by LAK cells. PHA was unable to markedly induce the LAK cell activity. Although both LAK and NK cell activity was decreased by mitomycin C treatment, their degree of susceptibility to such treatment was quite different. NK cells were more sensitive to mitomycin C than LAK cells. In contrast to the significant inhibition of the NK cell-mediated lysis by the addition of anti-CD 2 monoclonal antibody during cytotoxicity assay LAK cell-mediated lysis was not affected. These results indicate that LAK cells are capable of lysing a variety of tumor cells that are resistant to NK cells and their biological characteristics are also different.     

Inhibition by Fibrin Coagulation of Lung Cancer Cell Destruction by Human Interleukin-2-activated Killer Cells

We examined the effect of fibrin coagulation on tumor cytotoxicity mediated by human lymphokine (IL-2)-activated killer (LAK) cells. LAK cells were induced from peripheral blood mononuclear cells (MNC) by culture with recombinant IL-2 for 4 or 5 days, and LAK cell-mediated cytotoxicity against tumor cells was assessed by ⁵¹Cr release assay in the presence or absence of plasma from normal subjects and lung cancer patients. Plasma did not affect the phase of induction of LAK activity by IL-2, but dose-dependently inhibited the effector phase of LAK cell-mediated cytotoxicity against Daudi cells. Similar inhibition of LAK cell-mediated cytotoxicity was observed on pretreatment of Daudi cells and human lung cancer cell lines with human fibrinogen plus thrombin. A parallel relationship was found between the amount of fibrinogen in plasma of lung cancer patients and inhibition of LAK cytotoxicity. This inhibition was reduced by addition of anticoagulants (heparin or argatroban). These findings suggest that fibrin coagulation on tumor cells protects them from LAK cell-mediated tumor cytotoxicity in malignant lesions and that a combination of an anticoagulant drug and IL-2/LAK therapy may be effective for treatment of lung cancer patients.     

Release of Esterase from Murine Lymphokine-activated Killer Cells in Antibody-dependent Cellular Cytotoxic Reaction

Release of granule enzyme(s) (BLT esterase) in the antibody dependent lymphokine-activated killer (LAK) cell-mediated cytotoxic reaction (LAK ADCC) was studied using LAK cells induced from murine splenocytes and thymocytes, various human tumor cells and relevant monoclonal antibodies (mAbs) to the tumor cells. BLT esterase was not significantly released from LAK cells in direct LAK cell-mediated cytotoxic reactions (LAK CMC). However, cultures of LAK cells and IgG-coated target tumor cells resulted in release of the enzyme concomitantly with target cell lysis, although esterase release proceeded faster than target cell lysis. Anti-LFA-1 mAb showed an inhibitory effect on LAK CMC but not on either LAK ADCC or BLT esterase release in the ADCC. These results indicate that exocytosis of granule enzyme from LAK cells is triggered by stimulation of Fc receptor on LAK cells and that LAK CMC and LAK ADCC differ in their lytic mechanism in terms of the release of BLT esterase.     

Natural cytotoxicity in humans: susceptibility of freshly isolatd tumor cells to lysis

The cytotoxic potential of blood lymphocyters from healthy donors was tested against freshly isolated lung cancer cells and the erythroleukemia K562 cell line in short-term 51Cr release assays conducted at an effector:target ratio of 50:1. Most donors exhibited significant activity against K6-562 cells. By contrast, fresh tumor cells were refractory, only 6 of 30 showing significant cytotoxicity. The low susceptibility of these tumor cells was confirmed in third-party cold inhibition assays in which they interfered minimally with killing of K562 targets under conditions in which unlabeled K562 cells efficiently blocked cytotoxicity. Cells prepared from normal lung tissue and Raji cells also failed to inhibit killing. Although in comparison to the K562 cell line freshly isolated tumor cells were resistant, their susceptibility may not be so low as to be biologically irrelevant, inasmuch as boosting of natural killing activity by interferon induced levels of cytotoxicity against both types of target cell that were unattainable by unstimulated effectors. Interferon-boosted killers were lytic for "normal" lung cells and the Raji cell line.     

Characterization of Transendothelial Migratory Lymphokine-activated Killer Cells

We examined the killing activity of transmigrated lymphokine-activated killer (LAK) cells and their surface molecules associated with both transendothelial migration and cytotoxicity, using human umbilical vein-derived endothelial cell (HUVEC) monolayers on fibronectin with gelatin separating the upper chamber from the lower chamber. Migratory LAK cells were significantly more cytotoxic to Daudi target cells, expressed more LFA-1, and were more likely to be positive for CD2, compared to those LAK cells not adherent to the HUVEC monolayer. In contrast, in the absence of the HUVEC monolayer, there was no difference in LAK activity between migratory and non-adherent LAK cells. These results indicate that the interaction between LAK cells and the HUVEC monolayer allows selective migration of LAK cells with cytotoxic activity that is enhanced with respect to some surface molecules.     

Membrane-associated Lymphotoxin Expression and Functional Analysis of Lymphokine-activated Killer Cells Derived from Tumor-infiltrating Lymphocytes

The expression of a membrane-associated lymphotoxin molecule (mLT) on lymphokine-activated killer (LAK) cells obtained from 18 patients with malignant tumors and its role in the tumor cell killing mechanisms were investigated. LAK cells from tumor-infiltrating lymphocytes (TIL-LAK cells) were mainly composed of CD3-positive cells, whereas LAK cells from peripheral blood lymphocytes (PBL-LAK cells) were mainly composed of CD16- and CD56-positive cells. However, mLT was found to be expressed on TIL-LAK cells as well as PBL-LAK cells. The degree of mLT expression correlated with the killing activity of LAK cells towards L929 cells (r=0.806, P <0.01, n = 15), but not with that towards Daudi or K562 cells. Although the degree of mLT expression correlated with the amount of secreted lymphotoxin (LT) in the supernatant of LAK cell culture, the secreted LT itself could not account for the tumor cell killing activity of LAK cells. Polyclonal rabbit anti-LT antibody partially inhibited the killing activities of LAK cells towards L929 cells and this inhibition was found in the combination of autologous tumor cells and PBL-LAK cells. These findings suggest the possibility that the mLT-related cytotoxicity is involved in the tumor cell killing mechanisms of TIL-LAK cells as well as PBL-LAK cells.     

Role of fibrin coagulation in protection of murine tumor cells from destruction by cytotoxic cells

We have previously proposed that fibrin deposition on tumor cells during their migration in the blood could protect them from elimination by natural killer (NK) or other cytotoxic cells. Anticoagulant drugs could prevent fibrin coagulation and increase the efficiency of cytotoxic effector cells in tumor cell elimination. To further investigate the protective roles of fibrin, we studied in vitro the susceptibility of various murine tumor cells to the cytotoxic activity of NK or lymphokine activated killer (LAK) cells in the presence of murine plasma or serum. In the first set of experiments, tumor cells were incubated with plasma (at dilutions of 1:20-1:160) for 30 min before effector cells were added. Similarly, effector cells were first incubated with plasma before mixing with radiolabeled target cells for cytotoxicity assay. In some experiments target and effector cells and plasma were mixed simultaneously. The cytotoxic activity of both NK and LAK cells was inhibited if coagulation occurred around tumor-target or effector cells. Tumor cells were also protected when both target and effector cells were simultaneously mixed and trapped in the fibrin clot. Inhibition of the cytotoxic activity of effector cells against tumor cells was positively correlated with the level of fibrin clot formation. When the larger clot was formed and more radiolabeled tumor cells were trapped in the clot, the higher level of inhibition of cytotoxicity was observed. In contrast, serum did not affect the cytotoxic activity of NK or LAK cells. To exclude possible non-coagulation-related effects of plasma on LAK cells, a cytotoxicity series of experiments was performed using purified fibrinogen and thrombin. When fibrinogen and thrombin were preincubated with tumor cells or LAK cells or all components were admixed simultaneously, substantial protection of tumor cells from destruction by LAK cells was also observed. However, when heparin was added, fibrin coagulation was prevented and cytotoxic activity of LAK cells was restored. Inhibition of LAK cytotoxicity and protection of tumor cells by fibrin coagulation were mostly due to the prevention of tumor-effector cell conjugate formation. Adding plasma at postbinding time periods (15-30 min after mixing effector and target cells) did not affect the ability of LAK cells to kill tumor cells confirming that fibrin coagulation influenced the binding rather than the lytic phase of cytotoxic cell activity.     

Isolation of human lymphocyte antigens class I-restricted cytotoxic T lymphocytes against autologous myeloma cells.

Peripheral blood T cells from a patient with multiple myeloma in complete remission were selected in vitro against an autologous myeloma cell line (SBN-1), using a protocol designed for the selection of relatively rare precursor cytotoxic T cells (pCTL). Delayed addition (2 weeks) of interleukin 2 induced T-cell proliferation, and a bulk culture (T-cell line) was obtained 2 days later. This T-cell line displayed cytotoxicity against SBN-1. A CD8+ CD4- cytotoxic T-cell clone (CT5) was then obtained that recognized SBN-1 but not autologous EBV+ B-lymphoblastoid cells, autologous T PHA-blasts, or Daudi, Raji, K562, and 11 allogeneic myeloma cell lines. Moreover, CT5 cytotoxic activity against SBN-1 was blocked by monoclonal antibodies recognizing human lymphocyte antigen class I molecules. This seems to be the first demonstration of myeloma-specific pCTL in peripheral blood T cells of patients with multiple myeloma.     

Lymphokine activated killing of fresh human leukaemias

The relative susceptibility of 10 human leukaemias comprising acute phase leucocytes from 5 acute myeloid and 5 lymphoid neoplasms, and 2 immunoblastic lymphomas to killing by peripheral blood mononuclear cells (PBMC), before and after target cell treatment with phytohaemagglutinin (PHA), and by interleukin-2 (IL-2) activated peripheral blood lymphocytes (PBL) was investigated in short term 51Cr release assays using effector cells from 10 allogeneic donors. Optimal lectin-dependent cellular cytotoxicity (LDCC) was verified against K562 and L1210 cells and lymphokine-activated killing (LAK) against K562 and Daudi cells. Under these conditions, the majority of the leukaemias tested revealed only a finite sensitivity to any of the cytotoxic mechanisms, which was dependent on the donor origin of the effectors. The leukaemias were more consistently susceptible to LDCC than LAK and removal of adherent cells to enrich for the latter activity in effector populations, was ineffective. Lymphocytes from a patient in long term (greater than 5 yr) remission exhibited LAK against the autologous target E84, a natural killer (NK)-sensitive acute myelomonocytic leukaemia. These cells failed to cross-compete for lysis of K562 by LAK cells, suggesting the existence of different recognition structure(s) on the two targets.     

Cytotoxicity to tumor cells of monocytes from normal individuals and cancer patients

This study was aimed at characterizing the parameters which regulate human monocyte-mediated cytotoxicity to tumor cells as well as characterizing the target cell specificity, kinetics, etc., of the cytotoxic mechanism. Normal human peripheral blood monocytes were cytotoxic to tumor cells in an in vitro assay, measuring release of [³H]thymidine from human target cells. Monocyte cytolysis was observed with several adherent tumor lines including T24, a bladder cancer line; LR, a melanoma line; and an SV40-transformed W138 fibroblast line, with maximal cytolysis observed at 72 h. Lymphokines were not required to induce and only infrequently enhanced monocyte cytotoxicity. Prolonged exposure of monocytes to lymphokines or in vitro culturing of monocytes prior to lymphokine exposure did not alter the monocytes' response to lymphokine signals with respect to cytotoxicity. Lymphokines induced monocytes to exhibit enhanced spreading, suggesting that monocytes were susceptible to lymphokine signals but that the development of cytolytic function was independent of lymphokines. In contrast to the cytolysis of adherent tumor cells, monocytes were less effective in killing the non-adherent lymphoid target cells K562, Raji, and CEM. Monocytes were selectively cytotoxic to tumor cells and generally did not kill normal human fibroblast cell lines or PHA-stimulated lymphocytes. Monocytes from cancer patients exhibited normal cytotoxicity to several human tumor lines. Plasmas from some cancer patients were inhibitory to cytotoxicity mediated by both autologous monocytes and normal monocytes.     

APOPTOSIS OF TUMOR CELLS IN LECTIN－DEPENDENTLYMPHOKINE－ACTIVATED KILLER CELLMEDIATED CYTOTOXICITY

ＡＰＯＰＴＯＳＩＳＯＦＴＵＭＯＲＣＥＬＬＳＩＮＬＥＣＴＩＮ－ＤＥＰＥＮＤＥＮＴＬＹＭＰＨＯＫＩＮＥ－ＡＣＴＩＶＡＴＥＤＫＩＬＬＥＲＣＥＬＬＭＥＤＩＡＴＥＤＣＹＴＯＴＯＸＩＣＩＴＹＤｏｎｇＨａｉｄｏｎｇ董海东；ＸｉｎｇＲｏｎｇ邢嵘；ＧｕｏＬｉａｎｙｉｎ...     

健康人和骨肉瘤病人来源的LAK细胞体外抗瘤作用

采用５１Ｃｒ释放试验对健康人和骨肉瘤病人外周血单个核细胞（ＰＢＭ）在重组白细胞介素－２（ｒＩＬ－２）条件下，ＬＡＫ细胞的诱导形成及对４种传代瘤细胞的体外杀伤活性进行探讨。实验结果表明：２种来源ＬＡＫ细胞对Ｋ５６２（人慢性髓样红白血病细胞系）、ＳＭＭＣ７７２１（人肝癌细胞系）、ＬＡＸ（人肺腺癌细胞系）的杀伤活性均在５５％以上（按效靶比例５０：１），而对ＯＳ细胞（人骨肉瘤细胞系）的活性普遍低下，杀伤率低于３５％。结果证实：１）健康人和骨肉瘤病人的ＰＢＭ均能在ｒＩＬ－２条件下诱导形成具有广谱抗瘤活性的ＬＡＫ细胞群，二者的杀伤格局和效力相近。２）骨肉瘤细胞本身对ＬＡＫ细胞的杀伤作用存在强烈抗性。     

Antitumor effect of the plant alkaloid preparation, cepharanthin

The antitumor effect of cepharanthin (CR), a biscoclaurine alkaloid, was examined as to its direct action on tumor cells and inhibitory action on angiogenesis in tumors. The effect of CR on in vitro invasion by murine RL-[symbol: see text] 1 leukemia cells and Colon 26 tumor cells was studied using a biocoat matrigel invasion chamber. One hundred micrograms/ml of CR inhibited tumor cell invasion. Early induction of apoptosis was assayed by the binding of annexin V and phosphatidylserine (PS) in the cellular membrane CR (10 and 100 micrograms/ml) induced apoptosis in human Daudi and Raji B lymphoblastoid cells. Treatment with CR (1 and 10 micrograms/ml) also inhibited the in vitro growth of Daudi and Raji cells. Ten micrograms/ml of CR also inhibited the growth of human umbilical vein endothelial cells (HUVEC) and human dermal microvascular endothelial cells (HMVEC). These results indicate that CR has diversified antitumor functions, i.e., an enhancement of a sequential immune mechanism, a direct cytotoxic effect and inhibitory action of angiogenesis in tumors.     

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.