T helper cells are necessary for the eventual production of antibody from resting B cells. B cells may process antigen then present the metabolized product in the context of MHC Class II surface determinants to T cells. The T cell becomes activated leading to the synthesis and release of lymphokines which may promote B cell antibody synthesis. Questions surrounding this T cell-B cell cognate interaction concern: 1) the signal(s) transmitted by the cognate interaction though the T cell receptor to the T cell, and 2) the signal(s) delivered by the T cell to the B cell which would include those initiated by lymphokines. Murine T helper cells are divided into 2 main types depending on the what lymphokines are secreted in response to activation via the T cell receptor. Type I Th lymphocytes produce IL2 and Interferon-gama (IF-g), whereas type II th lymphocytes produce IL4. Helper function associated with an antibody response has been ascribed to type II helpers whereas type I helpers have been implicated in delayed type hypersensitivity reactions. It has been a point of controversy concerning whether a type I helper can induce resting B cells to become activated to produce antibody. The lack of helper function under these circumstances may be explained by what lymphokines are made and secreted. However, recent studies have suggested that the activation pathways utilized subsequent to signaling through the T cell receptor may be different between type I and type II helpers. Thus, there may also be differences in the way these two helper types initiate B cell activation via cognate interactions. To analyze Th function we propose to determine if the signaling to B cells by Th lymphocytes in a cognate interaction is different depending on the type of T helper cell.