The research proposed here would investigate cellular interactions involved in the immune response to viruses and viral antigens. An analysis of the development of the host defense against viruses and the cell types involved should allow insight into the natural response to these antigens and the possibility of manipulating that response. The cytotoxic T lymphocyte (CTL) has been shown to be important in the host response to infection in mice. These T cells are capable of lysing infected target cells which are identical at some region of the major histocompatibility complex. Cytotoxic T responses have been shown to be idependent upon helper T cells for their generation. These responses are influenced by suppressor T cells and are under the influence of Immune Response (IR) genes which affect the specificity and magnitude of the cytotoxic response. Examinig the T cell-T cell associations, especially as they relate to the genetic restrictions seen in this system, should allow dissection in some of the crucial cell-cell and antigen-cell interactions involved in the host responses to viruses. Antibodies are capable of specifically binding to T cell receptors. Such anti-idiotypic antibodies have been shown to have an important role in regulating host responses. We have used anti-idiotypic antibodies to stimulate viral immunity. An analysis of how these antibodies affect host defense and their possible use as immunizing agents is planned.