Short-term IgM memory is established within 1 day after primary injection. This 1 day priming is independent of cell division as it can take place in the pressence of methotrexate or hydroxyurea.
The primary response involves a similar 1 day nonproliferative phase. On the contrary, cells responding to a second injection of antigen after short priming intervals begin to proliferate within hours. This implies a qualitative difference between the antigen-sensitive cells in primed and normal animals.
After 1 day, further proliferative expansion of memory can occur, which is probably antigen dependent. The response to several dose regimens indicates that repeated antigenic contact is needed to maintain the IgM response.