IL4 and infection: Using the combination of the concentration of IFN-γ and IL-4 produced by MLN cells stimulated with parasitic female antigen as a measure of a Th1- and Th2-type response, respectively, this shows that rats infected with S. ratti alter their immune response from a Th1- to a Th2-type response as an infection progresses, with this change greater in animals infected with the highest doses (Fig. 2).