B7-2 is required for the progression but not the initiation of the type 2 immune response to a gastrointestinal nematode parasite

T cells require CD28/CTLA-4 costimulatory molecule interactions in addition to Ag-specific signals through the TCR for in vivo effector Th cell functi on. Some studies have suggested that the ligands for these costimulatory mo lecules may differentially influence effector T cell function,vith B7-2 fav oring a type 2 response and B7-1 favoring a type 1 response, while other st udies have suggested that these molecules may be redundant. The recent deve lopment of B7-2-deficient mice permits the direct analysis of the requireme nt of B7-2 during a type 2 immune response to an infectious pathogen, We ha ve examined, in B7-2-deficient mice, effector Th cell function and the asso ciated type 2 immune response following infection with Heligmosomoides poly gyrus, a natural murine parasitic nematode, Elevations in cytokine gene exp ression and protein secretion were pronounced and comparable in inoculated B7-2(-/-) and B7-2(+/+) mice at day 8 after H, polygyrus inoculation. Howev er, by day 14 after infection, increases in T cell cytokine expression were markedly inhibited in H, polygyrus-inoculated B7-2(-/-) mice. Furthermore, elevations in serum IgE and germinal center formation were inhibited at la ter stages of the immune response, while elevations in serum IgG1 persisted , These findings suggest that certain T-dependent components vary in their B7-2-dependency during the type 2 immune response. They further demonstrate that B7-2 interactions are not necessary for the initiation of the type 2 immune response, but are instead required for its progression after the dev elopment of effector T cells.