IFN-γ is associated with risk ofSchistosoma japonicuminfection in China

Immunology of human schistosomiasis

There is a wealth of immunologic studies that have been carried out in experimental and human schistosomiasis that can be classified into three main areas: immunopathogenesis, resistance to reinfection and diagnostics. It is clear that the bulk of, if not all, morbidity due to human schistosomiasis results from immune-response-based inflammation against eggs lodged in the body, either as regulated chronic inflammation or resulting in fibrotic lesions. However, the exact nature of these responses, the antigens to which they are mounted and the mechanisms of the critical regulatory responses are still being sorted out. It is also becoming apparent that protective immunity against schistosomula as they develop into adult worms develops slowly and is hastened by the dying of adult worms, either naturally or when they are killed by praziquantel. However, as with anti-egg responses, the responsible immune mechanisms and inducing antigens are not clearly established, nor are any potential regulatory responses known. Finally, a wide variety of immune markers, both cellular and humoral, can be used to demonstrate exposure to schistosomes, and immunologic measurement of schistosome antigens can be used to detect, and thus diagnose, active infections. All three areas contribute to the public health response to human schistosome infections.

Sex bias in the outcome of human tropical infectious diseases: influence of steroid hormones

Numerous investigations have revealed a bias toward males in the susceptibility to and severity of a variety of infectious diseases, especially parasitic diseases. Although different external factors may influence the exposure to infection sources among males and females, one recurrent phenomenon indicative of a hormonal influence is the simultaneous increase in disease occurrence and hormonal activity during the aging process. Substantial evidence to support the influence of hormones on disease requires rigorously controlled human population studies, as well as the same sex dimorphism being observed under controlled laboratory conditions. To date, only very few studies conducted have fulfilled these criteria. Herein, we introduce tropical infectious diseases, including amebiasis, malaria, leishmaniasis, toxoplasmosis, schistosomiasis, and paracoccidioidomycosis, in which hormones are suspected to play a role in disease processes. We summarize the most recent findings from epidemiologic studies in humans and from hormone replacement studies in animal models, as well as data regarding the influence of hormones on immune responses underlying the pathology of the diseases.

Invasive amebiasis: a microcirculatory disorder?

The two current models of invasive amebiasis both hold that direct contact of toxic molecules and amebas with tissue produces the necrotic areas characteristic of this disorder. Whereas one model characterizes these toxic molecules as amebic products (e.g., lectins, amebapores, cysteine proteinases and other proteolytic enzymes), the other describes them as products of the inflammatory response (e.g., cytokines, nitric oxide, reactive oxygen intermediates and cytotoxic granules). Both these models can account for necrotic areas with many amebas present and with acute inflammation, but not those with few or no amebas present or with scarce inflammation. A new model poses that an inadequate immune response leads to a continuous and prolonged activation of endothelial cells (ECs) by amebas, amebic molecules and cytokines, which triggers the mechanisms leading to necrosis. Other toxic molecules later contribute to EC activation: nitric oxide, reactive oxygen intermediates, the activated complement and proteases. Hyperactivated endothelial cells continuously express adhesion molecules (e.g., ICAM-1 and E-selectin), pro-coagulant molecules (e.g., tissue factor, von Willebrand factor, and the plasminogen activator inhibitor), resulting in ever greater inflammation and thrombosis, which eventually reduces or blocks blood flow in some vessels and starves certain tissue areas of an adequate oxygen and nutrient supply. When necrotic areas first develop, they are surrounded by inflammatory cells due to the acute inflammation at this stage. However, these cells are starved of oxygen and essential nutrients by the same microcirculatory dysfunction. The increasing concentration of nitric oxide during amebiasis eventually has an anti-inflammatory and vasodilating effect, creating a new mechanism for the microcirculatory dysfunction. This local microcirculatory dysfunction can explain necrotic areas in the presence of many, few, or no amebas, with abundant or scarce inflammation.

Immunohistochemical characterization of human fulminant amoebic colitis

In cases of fulminant amoebic colitis we have determined the interactions between Entamoeba histolytica trophozoites and immune cells in order to better understand the pathophysiology of amoebic colitis. Eleven specimens of amoebic colitis and five specimens of colon without amoebic lesions were studied. Trophozoites and immune cells were located by topographic stains, histochemistry and immunohistochemistry. Trophozoites were seen in both damaged and undamaged areas of the colonic mucosa. Specimens of fulminant amoebic colitis showed: (a) an increase in IgA+, IgG+ B cells and neutrophils; (b) a reduction in IgM+ B cells, CD8+ T cells, macrophages, eosinophils and mast cells; and (c) no change in the number of NK and CD4+ T cells. The cellular infiltrate in amoebic colitis may represent the combined effects of amoebic monocyte locomotion inhibitory factor and switching of IgM+ B cells to IgG+ and IgA+ plasma cells, induced by amoebic antigens. Tissue damage in the absence of trophozoites may result from ischaemia or host immune responses.