Regulation of the immune response in experimental and human schistosomiasis: the limits of an attractive paradigm

It is generally agreed that a major conceptual revolution in immunology began in 1986 when Mossman and his colleagues, by dividing mouse T helper cells (Th cells) into two populations with contrasting and cross-regulating cytokine profiles [38], deeply influenced our understanding of immunity to infectious and parasitic agents. Although it is always dangerous to oversimplify attractive paradigms, the complex interactions between hosts and schistosomes are now viewed, in their Various aspects, in the context of Th1 and Th2 cells. Granuloma formation, disease severity, and resistance to reinfection, which have all been shown to depend on immunological factors, are now being analyzed essentially within the perspective of Th1- and Th2-type responses. Indeed, most of the contributions to the present Forum clearly illustrate the current vision of immunoparasitology. To a significant extent, the respective roles of Th1 and Th2 cells became a dogma with calegorical statements leading to an apparently crystal-clear picture of the role of Th1 cells in protection and Th2 cells in immunopathology [43]. Schistosomiasis provides an exemplary illustration of the complexity of the Th1-Th2 paradigm and of its limits according to the model used. Human and rat studies on the one hand, and mouse studies on the other, have now reached strikingly different conclusions regarding the role of Th2 responses in protective immunity.