The specific IgM response in rats genetically selected for high or low serum IgM level.
The IgM response to SRBC in a line of rats selected for high serum IgM was higher and lasted longer than that in a line of rats selected for low IgM, while the response to TNP-LPS was similar at its peak in the two lines but persisted longer in the 'high' line. The difference between the lines is therefore more likely to be at the macrophage and/or the T cell level than at the B cell level.