antigen-stimulated d4 cells secreted helper factor ( s ) involved in the induction of cytotoxic t cells ( killer helper factor ( s ) , khf ) , and khf activity could be separated into two fractions , one with the m.w . of 15,000 to 20,000 and the other with the m.w . of 45,000 to 50,000 .
C0007634
cells
C1327616
secreted