Spent hops extract (Humulus Lupulus L.) attenuates inflammation and angiogenesis of the retina via the nuclear factor-kappaB and protein kinase B/extracellular signal-regulated kinase pathways.

Spent hops extract (SHE) is a plant extract containing compounds with proven anti-inflammatory and anti-angiogenic activities. However, extract may exert synergic effects compared to its individual polyphenol components. Inflammatory diseases of the retina may lead to visual impairment, a reduction of the comfort of life, and even blindness due to the formation of new pathological blood vessels. More effective therapeutic options are being sought. The goal of the present study was to investigate the anti-inflammatory and anti-angiogenic potentials of SHE on human retinal pigment epithelial cells (ARPE-19) stimulated by lipopolysaccharide (LPS) or tumor necrosis factor alpha (TNF-α). The SHE (250 µg/mL) was found to downregulate the gene expression of interleukin 6 (IL-6) to 33% in LPS-triggered cells; it also reduced both matrix metalloproteinase 2 (MMP-2) and 9 (MMP-9) mRNA expression to 13% and 43% respectively, and their activity to 82% (MMP-2) and 57% (MMP-9), compared to TNF-α-stimulated cells. Also, SHE modulated the TNF-α-induced expression of vascular endothelial growth factor (VEGF) and endothelial growth factor receptor 2 (VEGFR2). It is possible that SHE inhibited retinal inflammation and angiogenesis by suppressing the nuclear factor kappa B (NF-κB), protein kinase B (Akt) and extracellular signal-regulated kinase (ERK) pathways. Our results demonstrate that SHE has anti-inflammatory and anti-angiogenic potential against retinal diseases. This is the first such study to report on the efficacy of SHE on retinal inflammatory diseases.

Chemopreventive properties of spent hops (Humulus Lupulus L.) extract against angiogenesis, invasion and migration of colorectal cancer cells.

There is a great deal of interest in identifying new chemopreventive agents for colorectal cancer, one of the leading causes of cancer-related death. One promising group of candidates is the polyphenols; being natural compounds with high structural diversity, they have a very wide spectrum of anti-inflammatory, anti-oxidant and anti-cancer properties. The present study reports for the first time that spent hops extract (SHE) inhibits the angiogenesis, invasion and migration of SW-480 and HT-29 colorectal adenocarcinoma cells; after incubation with 200 µg/mL SHE, SW-480 and HT-29 cell invasion fell by 98.5% and 89% vs. controls, and migration was inhibited by 99% and 88% vs. controls. These changes were accompanied by a decline of matrix metalloproteinase 2 (MMP-2) and MMP-9 expression and activity. In addition, SHE reduced the expression of vascular endothelial growth factor and hypoxia-inducible factor 1α for both cell lines, indicating that the tested extract has anti-angiogenic potential. In conclusion, our data shows that SHE may be an effective chemopreventive agent acting via the inhibition of angiogenesis, invasion and migration of colorectal cancer cells.

Evaluation of phenolic composition, antioxidant and cytotoxic activity of aronia melanocarpa leaf extracts.

The objective of this study was to investigate the phytochemical composition, antioxidant and cytotoxic potential of aronia leaf crude phenolic-extract (ACE) and purified phenolic-rich extract (APE) on human intestinal cells (CCD 841 CoN) and colon cancer cells (SW-480 and HT-29). UPLC-Q-TOF-MS analysis confirmed that aronia leaves are rich in structurally diverse polyphenols (25 and 42 compounds for ACE and APE, respectively). Chlorogenic acid and quercetin-3-rutinoside were most abundant in both aronia extracts. The sum of detected polyphenols varied significantly between extracts ranging from 32.8 mg/g (ACE) to 436.3 mg/g (APE). The biological potential of aronia extracts was confirmed by applying in vitro antioxidant and cytotoxic assays. The results of antioxidant activity (ABTS and FRAP) indicate that APE showed 2-fold stronger antioxidant properties compared to ACE. APE revealed a stronger cytotoxic effect on SW-480 and HT-29 cells than ACE (MTT test). After 48 -hours of incubation, APE was found to inhibit SW-480 cell growth by 50% vs. control at 194.35 µg/mL, while for HT-29 cells it was observed at 552.02 µg/mL. In the case of ACE, IC50 has not been reached for SW-480 cells after 48 -hours of treatment, but for HT-29 it was 794.84 µg/mL. Moreover, the viability was significantly decreased in a concentration- and time-dependent manner for both cancer cell lines. Examined extracts showed selective inhibitory potential against colon cancer cells. However, after 72 h incubation with CCD 841 CoN cells, the obtained IC50 values for APE and ACE were 594 µg/mL and 709 µg/mL respectively. This suggests that aronia leaves are valuable natural-based products that may support the treatment as chemopreventive agents in colorectal cancer.

Chemoprotective effects of Japanese quince (Chaenomeles japonica L.) phenol leaf extract on colon cancer cells through the modulation of extracellular signal-regulated kinases/AKT signaling pathway.

Japanese quince leaf phenol-rich extract (PRE) represents a good source of phenolic compounds, among which chlorogenic acid and naringenin hexoside are the main constituents. The aim of this research was to evaluate the chemopreventive activity of PRE in human colon cancer (SW-480 and HT-29) and human normal colon cell line (CCD 841 CoN). All cell lines were exposed to different concentrations of the extract (150-500 κg/mL for SW-480 and CCD 841 CoN; and 250-750 κg/mL for HT-29) to investigate migration and invasion, as well as the activity and secretion of metalloproteinases (MMP-2 and MMP-9) involved in these mechanisms. Moreover, the influence of PRE on the activity of ERK and AKT pathways, which are strongly involved in colon cancer development (CRC), were measured. Our results demonstrated that PRE significantly inhibited migration and invasion in SW-480, HT-29 and CCD 841 CoN cells through MMP-2 and MMP-9-dependent mechanisms. We also proved that PRE can effectively downregulate both the activity and protein expression of MMP-2 and MMP-9 in these cell lines. The exception was the higher concentration of PRE, which up-regulated the protein expression of MMP-9 in SW-480. Additionally, we showed that significant inhibition of p-ERK/p-AKT expression in SW-480 after treatment with PRE is involved in chemopreventive effects of this extract. In case of exposure of HT-29 cells to PRE, we observed a significant upregulation of p-ERK protein expression, and suppression of p-AKT mechanism. This research of Japanese quince phenol leaf extract suggests its application in colon cancer prevention and treatment due to its ability to inhibit migration and invasion in MMP-9 and MMP-2-dependent mechanisms via most likely the modulation of ERK and AKT signaling pathways in colon cancer cells. Overall, our results provide an experimental foundation for further research on its potential activities and effects in vivo.

Osimertinib and anti-HER3 combination therapy engages immune dependent tumor toxicity via STING activation in trans.

Over the past decade, immunotherapy delivered novel treatments for many cancer types. However, lung cancer still leads cancer mortality, and non-small-cell lung carcinoma patients with mutant EGFR cannot benefit from checkpoint inhibitors due to toxicity, relying only on palliative chemotherapy and the third-generation tyrosine kinase inhibitor (TKI) osimertinib. This new drug extends lifespan by 9-months vs. second-generation TKIs, but unfortunately, cancers relapse due to resistance mechanisms and the lack of antitumor immune responses. Here we explored the combination of osimertinib with anti-HER3 monoclonal antibodies and observed that the immune system contributed to eliminate tumor cells in mice and co-culture experiments using bone marrow-derived macrophages and human PBMCs. Osimertinib led to apoptosis of tumors but simultaneously, it triggered inositol-requiring-enzyme (IRE1α)-dependent HER3 upregulation, increased macrophage infiltration, and activated cGAS in cancer cells to produce cGAMP (detected by a lentivirally transduced STING activity biosensor), transactivating STING in macrophages. We sought to target osimertinib-induced HER3 upregulation with monoclonal antibodies, which engaged Fc receptor-dependent tumor elimination by macrophages, and STING agonists enhanced macrophage-mediated tumor elimination further. Thus, by engaging a tumor non-autonomous mechanism involving cGAS-STING and innate immunity, the combination of osimertinib and anti-HER3 antibodies could improve the limited therapeutic and stratification options for advanced stage lung cancer patients with mutant EGFR.

Comparison of phenolic compounds, antioxidant and cytotoxic activity of extracts prepared from Japanese quince (Chaenomeles japonica L.) leaves.

Phenolic compounds are very important in the prevention and treatment of many civilization diseases, including colorectal cancer (CRC). In the present study we investigated and compared the phytochemical composition, antioxidant and cytotoxic activity of Japanese quince (Chaenomeles japonica L.) leaves crude phenolic extract (CPE) and purified phenolic-rich extracts (PRE). The UPLC-Q-TOF-MS analysis showed that both extracts contain diversified phenolics compounds (33 - 36 compounds in the PRE and CPE, respectively), among which chlorogenic acid and naringenin hexoside turned out to be the main constituents. Both FRAP and ABTS tests showed that PRE had 2-fold higher antioxidant activity compared to CPE. Furthermore, PRE exhibited a higher cytotoxic activity towards colon cancer cells (SW-480 and HT-29) than CPE. After 24-hours incubation with PRE the IC50 value for SW-480 cell line was obtained at the concentration of 239 µg/mL, while CPE treatment caused the same decrease only after 72h at 277 µg/mL. In addition, PRE had a stronger cytotoxic effect on the colon cancer cell lines (SW-480 and HT-29) than on normal intestinal cells (CCD-18Co and CCD 841 CoN). These results provide the first evidence that extracts from Japanese quince leaves (especially phenolic-rich extract, PRE) strongly decrease the viability of both SW-480 and HT-29 lines, which may suggest their cytotoxic activity towards colon cancer cells.

Spent hops (Humulus Lupulus L.) extract as modulator of the inflammatory response in lipopolysaccharide stimulated RAW 264.7 macrophages.

Macrophages play important roles in acute and chronic inflammation. Upon their activation, they secrete a variety of mediators, including eicosanoids, nitric oxide and cytokines, which play different roles in the stimulation and resolution of inflammatory processes. There is a continuous search for selective modulators of these processes. Natural polyphenols and polyphenol-rich extracts have been found to possess preventive and therapeutic potential, including by their anti-inflammatory effects. In this study, the inhibition of the formation of inflammatory mediators by the spent hops extract (SHE), a polyphenol-rich extract from Humulus Lupulus L., was examined using lipopolysaccharide (LPS)- activated murine macrophages (RAW 264.7). The SHE suppressed inter alia the interleukin-6 (IL-6) mRNA expression to 32% in LPS-activated macrophages and to 61% at a protein level (at 25 µg/mL). SHE reduced both the cyclooxygenase-2 (COX-2) mRNA expression to 47% and their protein expression to 32%. Not only did SHE inhibit the IL-6 and COX-2 levels but also decreased both inducible nitric oxide synthase (iNOS) protein expression to 2% at 25 µg/mL and nitric oxide (NO) production for all tested concentrations. The inhibited expression of these inflammatory molecules was likely caused by the reduced activity of nuclear factor-κB (NF-κB). Both mRNA and protein expression of NF-κB was decreased to 38% and 42%, respectively. These results provide the first evidence that SHE decreases the expression of proinflammatory cytokines and inflammatory mediators, which merits further studies to investigate the potential of SHE as anti-inflammatory preparation.

Japanese quince (Chaenomeles japonica) leaf phenol extract as modulator of the inflammatory response in lipopolysaccharide-triggered murine macrophage RAW 264.7 cells.

In the present study we investigated the anti-inflammatory activity of Japanese quince leaf polyphenol-rich extract (JQLPE) in lipopolysaccharide (LPS)-activated murine macrophages (RAW 264.7). The Q-PCR analysis revealed that JQLPE decreased Nfkb1, Ptgs2, and Il1b expression at the mRNA level by 80%, 50% and 48%, respectively. Similarly, JQLPE significantly attenuated expression of inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), interleukin-1beta (IL-1ß), IL-6 and tumor necrosis factor alpha (TNF-α) (by 60%, 50%, 67%, 37% and 36%, respectively) at the protein level and nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW264.7. Western blot also showed that the expression of nuclear factor kappaB (NF-κB) p65 and p-NF-κB p65 was down-regulated after JQLPE treatment. These results provide the first evidence that JQLPE decreases the expression of pro-inflammatory cytokines (IL-1ß, IL-6, TNF-α), inflammatory mediators (COX-2, iNOS) and both NF-κB p65 and p-NF-κB p65 in LPS-stimulated RAW264.7 cells, which may suggest its anti-inflammatory activity.

Polyphenol extract from evening primrose pomace alleviates experimental colitis after intracolonic and oral administration in mice.

Oenothera paradoxa (EP) preparations are commonly used in folk medicine to treat skin diseases, neuralgia, and gastrointestinal (GI) disorders. Several reports suggested that EP preparations exhibit potent anti-inflammatory and antioxidant activities both in vitro and in vivo. Here, we aimed to characterize the action of EP pomace polyphenol extract in mouse model of colitis. We analyzed the composition of EP pomace polyphenol extract using reversed phase HPLC system and ultra-performance liquid chromatography (UPLC) system coupled with a quadrupole-time of flight (Q-TOF) MS instrument. Then, we used a well-established animal model of 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis to determine the anti-inflammatory action of EP pomace polyphenol extract. We also investigated the effect of the EP pomace polyphenol extract on pro-inflammatory (IL-1ß and TNF-α) cytokine mRNA levels and hydrogen peroxide concentration in the inflamed colon. Administration of EP pomace polyphenol extract significantly improved macroscopic and microscopic damage scores, as well as myeloperoxidase (MPO) activity in TNBS-treated mice. The anti-inflammatory effect of the extract was observed after intracolonic and oral administration and was dose-dependent. Significant reduction of tissue hydrogen peroxide level after treatment with EP pomace polyphenol extract suggests that its therapeutic effect is a result of free radical scavenging. This novel finding indicates that the application of the EP pomace polyphenol extract in patients with inflammatory bowel diseases (IBDs) may become an attractive supplementary treatment for conventional anti-inflammatory therapy.

Antimicrobial activity of untypical lipid compounds in the cuticular and internal lipids of four fly species.

AIMS: This article describes the qualitative and quantitative analyses of untypical compounds in the cuticular and internal lipids of four dipteran species. For isolated compounds, antimicrobial activity against 18 reference strains of bacteria and fungi was determined. METHODS AND RESULTS: In this study, gas chromatography (GC) combined with mass spectrometry (GC-MS) was used to analyse the surface and internal compounds of four fly species. Seven untypical compounds from both pre-imaginal and imaginal stages of examined insects were identified. Azelaic acid (AA) was the most abundant, while phenylacetic and phenylpropionic acids occurred in lower concentration. Minor quantities of sebacic acid, 2-methyl-2-hydroxybutanoic acid, tocopherol acetate and trace amounts of 2,4-decadienal were also detected. Tocopherol acetate was found only in cuticular lipids of Musca domestica larvae. Each compound was tested against several species of fungi and bacteria by determining minimal inhibitory concentration (MIC). Human pathogenic fungi were also investigated. Phenylpropionic acid showed the greatest antifungal activity. Bacterial strains were insensitive to the presence of identified compounds, apart from 2,4-decadienal which strongly inhibited bacterial growth. CONCLUSIONS: This is the first time that the chemical composition and the antimicrobial activity of untypical compounds in the cuticular and internal lipids of four fly species has been analysed. SIGNIFICANCE AND IMPACT OF THE STUDY: Determination of untypical compounds and their antimicrobial activity can effectively contribute to the knowledge concerning insect defence mechanisms.

Detection and quantification of Plectosphaerella cucumerina, a potential biological control agent of potato cyst nematodes, by using conventional PCR, real-time PCR, selective media, and baiting.

Potato cyst nematodes (PCN) are serious pests in commercial potato production, causing yield losses valued at approximately $300 million in the European Community. The nematophagous fungus Plectosphaerella cucumerina has demonstrated its potential as a biological control agent against PCN populations by reducing field populations by up to 60% in trials. The use of biological control agents in the field requires the development of specific techniques to monitor the release, population size, spread or decline, and pathogenicity against its host. A range of methods have therefore been developed to monitor P. cucumerina. A species-specific PCR primer set (PcCF1-PcCR1) was designed that was able to detect the presence of P. cucumerina in soil, root, and nematode samples. PCR was combined with a bait method to identify P. cucumerina from infected nematode eggs, confirming the parasitic ability of the fungus. A selective medium was adapted to isolate the fungus from root and soil samples and was used to quantify the fungus from field sites. A second P. cucumerina-specific primer set (PcRTF1-PcRTR1) and a Taqman probe (PcRTP1) were designed for real-time PCR quantification of the fungus and provided a very sensitive means of detecting the fungus from soil. PCR, bait, and culture methods were combined to investigate the presence and abundance of P. cucumerina from two field sites in the United Kingdom where PCN populations were naturally declining. All methods enabled differences in the activity of P. cucumerina to be detected, and the results demonstrated the importance of using a combination of methods to investigate population size and activity of fungi.

Synthesis and antitumor activity of conjugates of muramyldipeptide, normuramyldipeptide, and desmuramylpeptides with acridine/acridone derivatives.

The synthesis of two groups (Chart 1, types A and B) of conjugates of MDP (muramyldipeptide) and nor-MDP (normuramyldipeptide) with acridine/acridone derivatives and the synthesis of analogues of desmuramylpeptides (Chart 1, types C and D) containing acridine/ acridone derivatives have been described. In type A conjugates, the hydroxyl group at C6 of the sugar moiety was acylated with acridine/acridone N-substituted omega-aminoalkanocarboxylic acids (Scheme 1), whereas the conjugates of type B (Table 2) and three analogues of type C or D (Scheme 2) have an amide bond formed between the carboxylic group of isoglutamine and the amine function of the respective acridine/acridone derivatives. The preliminary screening data indicate that the analogues of groups A, C, and D exhibit small cytotoxic activity, whereas several analogues of type B, 4b, 4c, 4e, 4g, 4h, 4i, and 4l, exhibiting potent in vitro cytotoxic activity against a panel of human cell lines (Table 4), have been selected by the National Cancer Institute (NCI) Evaluation Committee for further testing. Analogues 4b and 4h were active in the in vivo hollow fiber assay (Table 5). Analogue 3a shows an immunostimulating effect on the cytotoxic activity of the NK cells obtained from the spleen of healthy and Ab melanoma bearing animals.

Mechanisms of Mycobacterium avium pathogenesis.

Infections caused by Mycobacterium avium are common in AIDS patients and patients with chronic lung diseases. The bacterium can be acquired both through the intestinal route and respiratory route. M. avium is capable of invading mucosal epithelial cells and translocating across the mucosa. The bacterium can infect macrophages, interfering with several functions of the host cell. The host defense against M. avium is primarily dependent on CD4+ T lymphocytes and natural killer cells. Activated macrophages can inhibit or kill intracellular bacteria by mechanisms that are currently unknown, but M. avium can invade resting macrophages and suppress key aspects of their function by triggering the release of transforming growth factor beta and interleukin 10. Co-infection with HIV-1 appears to be mutually beneficial, with both organisms growing faster.

Nitrotyrosine formation after activation of murine macrophages with mycobacteria and mycobacterial lipoarabinomannan.

Murine peritoneal macrophages, elicited with thioglycollate, were stimulated in vitro with lipopolysaccharide (LPS). The production of nitrite, superoxide anion (SOA), and the accumulation of nitrotyrosine in the cells increased after treatment, and all were inhibitable by the NO synthase inhibitor NG-monomethyl-L-arginine monoacetate (L-NMMA). This effect suggests a direct correlation between the accumulation of those metabolites and NO synthase activity. Lipoarabinomannan (LAM) purified from Mycobacterium tuberculosis was added to peritoneal macrophages in the presence of interferon-gamma (IFN-gamma); the cells produced nitrite and SOA, both inhibitable by L-NMMA. There was, as well, accumulation of nitrotyrosine in the macrophage proteins. Strikingly, the amount of nitrotyrosine measured after LAM plus IFN-gamma, or LAM plus the low molecular weight adjuvant glutamylmuramyl dipeptide (GMDP), increased significantly in the presence of L-NMMA. These results suggest that murine macrophages, upon LAM stimulation, might generate reactive nitrogen metabolites by a route other than NO synthase. Nitrotyrosine accumulation after infection of macrophages in vitro, with either live bacille Calmette-Guérin (BCG) or live M. tuberculosis, in the presence or absence of IFN-gamma, showed no correlation with nitrite production, suggesting a low superoxide production.

Suppression of growth of Bomirski Ab melanoma and its metastasis in hamsters by angiogenesis inhibitor TNP-470.

The growth of solid tumors and their metastasis is dependent on the development of new blood vessels (angiogenesis). In this study, we examined the effect of the angiogenesis inhibitor TNP-470 on a fast growing melanoma in hamsters. The effect was observed both on tumor growth and metastasis. Treatment with TNP-470 caused a significant decrease in the rate of tumor growth and suppression of the development of metastasis in 63% of treated animals. Some of the hamsters treated with TNP-470 had the tumor excised and the effect of that operation on the development of metastasis was examined. In such cases the inhibitory effect of TNP-470 was weaker than in tumor bearing animals. This indicates that excision of tumor created more favourable conditions for angiogenesis and that the dose of TNP-470 should be increased to be effective in such conditions.

The in vitro effect of new muramyl peptide derivatives on cytotoxic activity of NK (natural killer) cells from hamsters bearing Ab Bomirski melanoma.

The modulation of NK activity by muramyl dipeptides derivatives against Ab (amelanotic) Bomirski melanoma and human erythroleukemia K562 cells was studied in vitro. The stimulatory effect was observed for 3 of 7 muramyl dipeptides: MDP(L-Ala)C921, MDPC857 and L18-MDP(Ala) in relation to cytotoxic activity of NK cells obtained from peripheral blood and spleen of healthy and Ab Bomirski melanoma bearing hamsters. An increased of cytotoxic activity NK cells isolated from animals before and during the transplantable phase of the tumor against K562 was found. A similar stimulation was received for NK cells obtained from animals against their own melanoma cells. The most significant influence of examined MDP derivatives on the cytotoxic activity of NK cells were obtained from animals between 10 to 12 days of tumor growth. The extent of the modulation of cytotoxic activity of NK cells was dependent on its initial value both in healthy control and Ab Bomirski melanoma bearing hamsters. If natural cytotoxic activity was high the stimulatory effect of the examined MDP derivatives was only slightly expressed.

Effect of tumor excision on NK cytotoxic activity and formation of metastases of Bomirski melanoma in hamsters.

The growth of transplanted Bomirski melanoma in hamsters is accompanied by the decrease of natural killer cytotoxic activity and the formation of metastases. The excision of primary tumors was carried out to examine what was the effect of the growing tumor and its metastases on the host's NK activity. It was found that the excision of primary tumor caused increased NK cytotoxic activity in comparison to that of nonoperated animals although it was still lower than that of healthy hamsters. It is concluded that both, a growing tumor and metastases, exert suppressive effects on NK activity and those effects add up. The pattern of metastases in operated animals was different to that observed in nontreated hamsters.

Changes of natural killer cytotoxic activity and natural killer sensitivity during growth of Bomirski melanotic (Ma) and amelanotic (Ab) melanomas.

Natural killer (NK) cytotoxic activity during the growth of melanotic (Ma) and amelanotic (Ab) variants of Bomirski hamster melanoma, in the blood and the spleen, was examined. The melanoma variants differed in their growth rate and metastatic pattern. Ability to form conjugates by effectors with targets and cytotoxic effects were compared. As targets K562 cells and tumor cells were used. It was found that during the growth of Ma melanoma activity of NK cells was not changing but the sensitivity of tumor cells was decreasing. However, during growth of Ab melanoma both NK activity and NK sensitivity were reduced.

[Muroctasin, a muramyl dipeptide derivative]. / Muroctasin, pochodna muramylodipeptydu.

This paper presents a review of studies on the metabolism, pharmacological and clinical properties of a new synthetic muramyl dipeptide derivative N2-/(N-acetylmuramoyl)-L-alanyl-D-isoglutaminyl/-N6-stearoyl-L-lysine(MD P- Lys(L18), muroctasin). Due to its effect on the number of peripheral blood leukocytes this compound is expected to be a useful drug for the treatment of leukopenia induced by cancer chemotherapy or radiation therapy.

Monocytes are responsible for depressed natural killer (NK) activity in both young and elderly low NK responders.

Two age groups--young (19-35) and elderly (70-91)--were compared with respect to natural killer (NK) cytotoxic activity. In both groups, low and high NK responders could be distinguished. Low NK responders constituted about 70% of all elderly and 40% of young individuals. The differences in the magnitude of NK activity among the young and elderly groups could only be observed when peripheral-blood mononuclear cells but not peripheral-blood lymphocytes were used as effector cells in a 51Cr release assay. Experiments with removal or addition of graded numbers of monocytes showed that these cells were responsible for the low level of NK activity in both the young and elderly low NK responders.