Maturation of b lymphocytes in rates. III. Two subpopulations of memory B cells in the thoracic duct lymph differ by size, turnover rate, and surface immunoglobulin.

We examined the ability of large and small thoracic duct cells obtained from Lewis rats primed to DNP to restore the adoptive secondary anti-DNP response in irradiated syngeneic hosts given an excess of T helper cells. The large cells were four to five times more active on a per cell basis than were the small cells. However, the large cells constitute only 7 to 8% of the thoracic duct cells and, therefore, make a minor contribution to the restorative activity of the unfractionated cells. Pretreatment of thoracic duct cell donors with high specific activity 3H-TdR for 48 hr before cannulation markedly reduced the memory B cell activity of the large cells, but had little effect on that of small cells. In addition, the activity of the large cells diminished with time after primary immunization, but that of the small cells remained stable. Immunofluorescent staining of the large and small cells for surface IgM and IgG, and subsequent sorting on the fluorescence-activated cell sorter (FA CS), showed that surface IgM was present on large memory B cells, and that IgG was present on small memory B cells. The experimental results suggest that two subpopulations of memory B cells in the thoracic duct lymph differ by size, rate of turnover, persistence after primary immunization, and class of surface IgG.