Interleukin-5 is the predominant cytokine produced by peripheral blood mononuclear cells in alveolar echinococcosis.

An involvement of cellular immunity in alveolar echinococcosis is strongly suggested by the intense granulomatous infiltrations observed around the hepatic parasite lesions. However, the basis of cellular immunoregulation in patient with alveolar echinococcosis is poorly understood. The present report shows a comparative analysis of lymphoid cell function in peripheral blood mononuclear cells (PBMC) of 16 patients with alveolar echinococcosis and of healthy individuals. Our in vitro restimulation studies with crude Echinococcus multilocularis antigen demonstrated that PBMC from patients with alveolar echinococcosis were responsive to challenge with parasitic antigen as measured by lymphoid cell proliferation. In this system, we also evaluated cytokine expression at the gene and protein levels after stimulation with E. multilocularis antigen. Analysis of cytokine mRNA expression revealed distinct patterns of cytokine expression in patients and normal donors. By using reverse transcriptase PCR, we could demonstrate that the TH1 cytokine transcripts interleukin-2 (IL-2) and gamma interferon (IFN-gamma) are present in PBMC from patients with alveolar echinococcosis. Moreover, it was found that stimulation with E. multilocularis antigen induced or enhanced the expression of the TH2 cytokine IL-3, IL-4, IL-10, and especially IL-5 mRNAs in PBMC from 13 of 16 patients with alveolar echinococcosis. Two patients who were examined after radical surgery, as well as another patient with a stable course of the disease under continuous chemotherapy, were not able to generate the same pattern of cytokine response and had no evidence of IL-5 mRNA synthesis. In contrast to the frequent expression of TH2 cytokine mRNAs observed in patients with alveolar echinococcosis, PBMC cultures from normal donors showed prominent IL-2 and IFN-gamma mRNA expression but weak IL-3, IL-4, and IL-10 mRNA expression. Most interestingly, IL-5 mRNA was substantially absent in PBMC from healthy individuals. In accordance with the mRNA studies, it was found that E. multilocularis antigen induced the secretion of large amounts of IL-5 and intermediate amounts of IFN-gamma in patients with alveolar echinococcosis, whereas large amounts of IFN-gamma and no or threshold amounts of IL-5 were detected in supernatants from healthy individuals. Collectively, the present study provides the first evidence that a TH2 immune response is gradually activated during the course of E. multilocularis infection, indicating a critical role for IL-5 in the manifestation of human alveolar echinococcosis.