Rabbit lymph node fragments undergoing an anamnestic response in vitro produce both 7 S (IgG) and 19 S (IgM) antibodies as well as inconstant amounts of 28 S antibodies that are presumably of IgM type. The majority of the antibodies produced are of the 7 S type, which, after 15 days of culture, can represent more than 90% to 99% of the antibody activity in the fluids; however, small amounts of 19 S antibodies can be present for up to 15 days in these culture fluids. While the absolute amounts of antibody activity, radioactivity incorporated and protein increased over the course of these experiments, it is inferred that antibody is only a relatively small percentage of the newly synthesized protein that is present in the culture fluids
