| Abstract: | Wehn normal mouse spleen or lymph node cells are cultured for 7 days in agar-medium containing 2-mercaptoethanol and sheep red blood cells (SRBC), approximately one B lymphocyte colony (BLC) develops per 50-100 cells seeded. Incubation of cultures for 3 h with guinea-pig complement at day 7, demonstrated that 0.05-0.25% of all BLC form specific antibody against SRBC (SRBC-AF-BLC). The SRBC specific colonies appear centrally in lytic plaques of 2-5 mm in diameter and cells recovered from individual SRBC-AF-BLC were shown to produce antibodies of the IgM class against SRBC. Cells forming SRBC-AF-BLC are absent in the new-born and infantile spleen but appear in adult mice with a frequency of 5, 10-25 and 25-70 per 10(6) bone marrow, spleen and lymph node cells respectively. specific immunization in vivo or in vitro does not greatly affect the number of SRBC-AF-BLC-forming cells. Cytolysis of spleen cells with anti-Ig serum plus complement prior to culture reduced the number of total BLC and that of specific SRBC-AF-BLC by 93% and 94% respectively. The peak sedimentation velocity of both SRBC-AF-BLC-forming cells and total BLC-forming cells was 3.5 mm/h. Spleen cells enriched 200-300 times for cells that bind specifically to the hapten NIP were not enriched for cells forming colonies with specific antibody production against NIP. The data indicate that the cells that give rise to specific antibody-forming colonies belong to a mature virgin B cell group of small Ig-positive B lymphocytes. |
