1. From the Departments of Medicine (L.J.P, G.S., J.A.B.), Experimental Pathology (L.J.P., M.C.F., J.A.B.), Surgery (M.P.F.), and Microbiology and Immunology (M.P.F.), University Of California Los Angeles; Department of Immunology (N.K., L.K.C., W.A.B.), The Scripps Research Institute, La Jolla; and the Division of Developmental Immunology (H.C.), The La Jolla Institute For Allergy and Immunology, San Diego, Calif.