Several cytokines play significant roles in the development and pathogenesis of pleural effusion. Little is known, however, about possible interactions between individual cytokines in terms of regulation of their relative abundance in the effusion. We studied 93 patients presenting with pleural effusion to the National Sanyo Hospital (68 men and 25 women; mean age, 64 years). Twenty-two patients had tuberculous pleurisy, 40 had malignant pleuritis, and 31 had effusions due to an etiology other than tuberculosis or cancer (miscellaneous). Pleural fluid concentrations of IL-2, IL-4, IL-5, IL-10, TNF-α, and INF-γ were simultaneously measured by cytometric bead array (CBA). The ratios of IL-4/IL-5, IL-4/TNF-α, IL-2/TNF-α, and IL-10/TNF-α were lower in patients with tuberculosis pleurisy compared with other patients. In all three groups of patients significant correlation was seen between abundance of IL-2 vs. IL-4, IL-5, IL-10, or TNF-α, between IL-4 vs. IL-10, and between TNF-α vs. INF-γ. In malignant pleural fluid patients, the significant correlation was between IL-2 vs. IL-4, TNF-α, or INF-γ, between IL-4 vs. INF-γ, and between TNF-α vs. INF-γ. In tuberculosis pleural fluid patients, the significant correlation was between IL-2 vs. TNF-α, between IL-4 vs. IL-10, and between TNF-α vs. INF-γ. In miscellaneous pleural fluid patients, the significant correlation was between IL-2 vs. IL-4, IL-10, or TNF-α, between IL-4 vs. IL-10, TNF-α, and between IL-10 vs. TNF-α. No significant correlation was observed between other pairs of cytokines. Strong correlation in abundance between particular cytokines in pleural fluids suggests cross-talk between them, in terms that an altered level of one of them provides a feedback mechanism regulating synthesis and/or secretion of another one. Such interactions may play important roles in pathogenesis and severity of the effusion. The CBA methodology provides a convenient tool to investigate these interactions.

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