The role of suppressor T cells will be further studied. The subset of normal suppressor T cells from SJL mice and other strains will be studied for the presence of different Ia determinants. The interaction of syngeneic T cells from spleens of unprimed animals with T and B cells from spleens of primed animals will be investigated. As unprimed splenic T cells bring about IgE antibody suppression, it will be investigated if these cells interact with IgE producing B cells, IgE specific helper T cells or eventually with a subset of IgE Suppressor T cells which by themselves without interaction with unprimed T cells are unable to bring about IgE antibody suppression. The substances extracted from unprimed T cells will be further characterized, as for molecular size, presence or absence of Ia determinants on this substance, and methods of purification will be used to obtain a better characterized substance of which the chemical properties may be studied. The action of the IgE hybridoma in vivo on syngeneic mice will be studied with respect to Fc receptor presence and/or development on different cell types.