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Apigenin and its structural analogues chrysin and luteolin were used to evaluate their capacity to inhibit the production of pro-inflammatory cytokines by lipopolysaccharide (LPS)-stimulated human peripheral blood mononuclear cells (PBMC). Furthermore, flowcytometric analysis was performed to compare the effects of apigenin, chrysin, luteolin, quercetin and naringenin on the different cell types present in PBMC. LPS-stimulated PBMC were cultured in the presence of the flavonoids and TNFalpha, IL-1beta and IL-6 were measured in the supernatants. In parallel, metabolic activity of the PBMC was determined by measuring succinate dehydrogenase activity. Apigenin, chrysin and luteolin dose-dependently inhibited both pro-inflammatory cytokine production and metabolic activity of LPS-stimulated PBMC. With increasing concentration of apigenin, chrysin or luteolin the monocytes/macrophages disappeared as measured by flowcytometry. This also appeared to occur in the non-LPS-stimulated PBMC. At the same time there was an increase in dead cells. T- and B-lymphocytes were not affected. Quercetin and naringenin had virtually no effects on cytokines, metabolic activity or on the number of cells in the studied cell populations. In conclusion, monocytes were specifically eliminated in PBMC by apigenin, chrysin or luteolin treatment in vitro at low concentrations (around 8 microM), in which apigenin appeared to be the most potent.

To determine the effects of EPA, stearidonic acid (STA) or gamma-linolenic acid (GLA) on immune outcomes, healthy male subjects consumed one of seven oil blends for 12 weeks. EPA consumption increased the EPA content of peripheral blood mononuclear cells (PBMC). Consumption of GLA (2.0 g/d) in the absence of STA or EPA increased di-homo-GLA content in PBMC. Neither STA nor its derivative 20 : 4n-3 appeared in PBMC when STA (<1.0 g/d) was consumed. However, STA (1.0 g/d), in combination with GLA (0.9 g/d), increased the proportion of EPA in PBMC. None of the treatments altered neutrophil or monocyte phagocytosis or respiratory burst, production of inflammatory cytokines by monocytes, T lymphocyte proliferation or the delayed-type hypersensitivity response. Production of cytokines by T lymphocytes increased in all groups, with no differences among them. The proportion of lymphocytes that were natural killer cells decreased significantly in subjects receiving 2.0 g EPA or GLA/d. There were no other effects on lymphocyte sub-populations. Plasma IgE concentration decreased in most groups, but not in the control group. Plasma IgG2 concentration increased in the EPA group. Thus, EPA or GLA at a dose of 2.0 g/d have little effect on key functions of neutrophils, monocytes and T lymphocytes, although at this dose these fatty acids decrease the number of natural killer cells. At this dose EPA increases IgG2 concentrations. STA can increase immune cell EPA status, but at 1.0 g/d does not affect human immune function.

Dietary oils (such as borage oil), which are rich in gamma-linolenic acid (GLA), have been shown to be beneficial under inflammatory conditions. Dihomo-GLA (DGLA) is synthesized directly from GLA and forms a substrate for cyclooxygenase (COX) enzymes, resulting in the synthesis of lipid mediators (eicosanoids). In the present study, the immunomodulatory effects of DGLA were investigated and compared with those of other relevant fatty acids. Freshly isolated human peripheral blood mononuclear cells (PBMC) were cultured in fatty acid (100 microm)-enriched medium for 48 hr. Subsequently, cells were stimulated with lipopolysaccharide (LPS) for 20 hr and the cytokine levels were measured, in supernatants, by enzyme-linked immunosorbent assay (ELISA). Phospholipids were analysed by gas chromatography. Fatty acids were readily taken up, metabolized and incorporated into cellular phospholipids. Compared with the other fatty acids tested, DGLA exerted pronounced modulatory effects on cytokine production. Tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-10 levels were reduced to 60% of control levels, whereas IL-6 levels were not affected by DGLA. Kinetic studies showed that peak levels of TNF-alpha, occurring early after LPS addition, were inhibited strongly, whereas IL-10 levels were not affected until 15 hr after stimulation. Both the reduction of cytokine levels and the decrease in arachidonic acid levels in these cells, induced by DGLA, were dose dependent, suggesting a shift in eicosanoid-subtype synthesis. However, although some DGLA-derived eicosanoids similarly reduced TNF-alpha levels, the effects of DGLA were probably not mediated by COX products, as the addition of indomethacin did not alter the effects of DGLA. In conclusion, these results suggest that DGLA affects cytokine production by human PBMC independently of COX activation.