Study objective: Human immunity has been found to have two major components, cellular and humoral immunity. T-helper type 1 (Th1) pathway favors cellular immunity and Th2 pathway favors humoral immunity. Early determination toward Th1 and Th2 cells in the immune response is dependent on the balance between interleukin-12 (IL-12), which favors Th1 responses, and IL-4, which favors Th2 responses. IL-2 and interferon-γ (IFN-γ) are produced in the Th1 pathway, and IL-4 and IL-10 are produced in the Th2 pathway. Lack of cellular immunity, IL-2, and IFN-γ had been reported in malignant pleural effusions. However, to our-knowledge, there are no previous reports on other cytokine components involving Th1 or Th2 pathway. The present study was designed to answer these questions. Design: Cytokine levels in peripheral blood and pleural fluid of 21 patients with malignant pleural effusion, including IL-4, IL-10, and IL-12, were analyzed with enzyme-linked immunosorbent assays. Lymphocyte subpopulations of peripheral blood and pleural effusion were also studied by using flow cytometry. Measurements and results: The results showed a significant increase in IL-10 level as compared with blood samples. IL-4 and IL-12 were below minimal detectable concentrations both in the blood and the effusion. The ratio of pleural helper T cells was significantly higher than in the blood (p=0.0002). The ratio of pleural natural killer (NK) cells was significantly lower than in the blood (p=0.0001). The ratio of pleural suppressor T cells was lower than blood with borderline significance (p=0.0522). No significant change in B- lymphocyte ratio between blood and pleural effusion was found (p=0.2471). There was no correlation between difference in IL-10 level and lymphocyte subpopulation of pleural effusion and blood samples. Conclusions: Helper T- cell subpopulations were increased while NK and suppressor T-cell subpopulations were decreased in malignant pleural effusions. The decrease in NK cell subpopulations with elevated IL-10 and minimal IL-12 concentration in neoplastic pleural effusion would suggest the usage of IL-12 or antibody of IL-10 to improve local cellular immunity. Further study is needed.
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