Cellular immune response in Echinococcus multilocularis infection in humans. II. Natural killer cell activity and cell subpopulations in the blood and in the periparasitic granuloma of patients with alveolar echinococcosis.

In animal models, the development of Echinococcus multilocularis larvae has been shown to correlate with the immune status of the host, and particularly with cellular immunity. In humans, a defect in immune regulation may explain the persistence of cellular infiltration and fibrogenesis. We assessed natural killer (NK) activity in the peripheral blood mononuclear cells (PBMC) of patients with alveolar echinococcosis, and compared in 12 patients who underwent a surgical procedure the cell populations in the PBMC with those present in the periparasitic granuloma. The results indicated that (i) the NK cell activity of the PBMC was significantly altered at the lower NK cell: target cell ratios; (ii) the percentage of CD8+ cells was significantly decreased in the PBMC with an increased CD4:CD8 cell ratio; (iii) inversely, the CD8+ cells constituted the main population of T cells in the liver of most patients; and (iv) the periparasitic granuloma was mainly composed of macrophages, T cells and myofibroblasts in close association with the developing fibrosis. A relatively high number of CD4+ cells in the periparasitic granuloma of two patients with 'abortive' parasitic lesions suggested that, as it is observed in experimental E. multilocularis infection, differential evolution of the phenotypic pattern of the periparasitic granuloma could be related to resistance or sensitivity to infection by E. multilocularis in humans.