Abstract: The present invention relates to genes and their encoded proteins which induce immunological effector cell activation and chemattraction. The proteins of the invention attract subsets of immunological effector cells and stimulate them to express their specialized effector cell functions. Such proteins, termed Ap-1 proteins, are expressed by lymphoid cells, and bind to effector cells such as macrophages and mast cells. In particular, the Ap-1 proteins induce macrophage phagocytosis, expression of class II major histocompatibility molecules, cytotoxicity, and migration, and induce hematopoietic progenitor cell differentiation. The Ap-1 molecules can be of value in the therapy or diagnosis of inflammatory or immune disorders, or neoplasia.