Digenetic trematodes: multiplication of the intramolluscan stages in some species is potentially unlimited.

By carrying out chain-transplantations of intramolluscan stages of digeneans from infected to uninfected snails it has been demonstrated that a great number of generations of these stages can follow one another. In Echinostomatids the succession of redial generations potentially seems to be unlimited.

Selective in vivo suppression of T lymphocyte responses in experimental measles virus infection.

During and after measles virus (MV) infection humans are highly susceptible to opportunistic infections because of a marked immunosuppressive effect of the virus. The mechanisms by which the virus induces this phenomenon is not well understood. In particular, detailed information is missing on the targets of suppression in relation to antigen-specific T and B cell responses. Because such studies require animal experiments, we used the cotton rat model, in which the MV causes a respiratory tract infection. Primary as well as secondary T cell responses were impaired in vivo and ex vivo by MV infection. The proliferation of T cells was greatly reduced, but their effector functions, such as cytolysis or cytokine secretion, were not. In contrast, primary and secondary B cell responses in vivo as measured by the frequency of antigen-specific plasma cells in an enzyme-linked immunospot (ELISPOT) assay were not altered by MV infection. Only the secretion of immunoglobulins was reduced slightly in animals primarily infected with MV after 2 weeks. These data demonstrate that MV-induced immunosuppression acts primarily on the T cell responses in vivo.