Heterogeneity of antibodies produced by single hemolytic foci

Abstract

Lethally irradiated male BDF 1 mice were injected with 10 7 bone marrow cells, 8 × 10 5 spleen cells, and sheep or goat red blood cells as antigens. The cross-reactivity between these red blood cells is approximately 40%, as determined by injecting normal mice with either sheep or goat red blood cells, removing their spleens 4 days later, and assaying all spleens for both antisheep and antigoat plaque-forming cells. Eight days after injection of bone marrow, spleen, and antigen, the spleens of the irradiated recipients were removed and assayed for the presence of hemolytic foci by the Playfair technique, and were found to contain an average of 0.7 foci/spleen. Earlier studies had demonstrated that such foci could contain plaque-forming cells derived from more than one precursor cell. The positive pieces comprising a single hemolytic focus were removed, pooled, and aliquots were assayed for direct and indirect plaque-forming cells to the immunizing antigen. Several foci were found to contain 17–82% as many plaque-forming cells lysing the cross-reacting antigen as lysed the immunizing antigen. These data indicate that these foci contained plaque-forming cells of two specificities: (1) plaque-forming cells which responded to determinants on the immunizing antigen only, and (2) plaque-forming cells which responded to determinants on both the immunizing and cross-reacting antigens. In addition, single foci were found which contained both direct and indirect plaque-forming cells lysing the immunizing antigen. Sixteen of 39 foci assayed contained more than twice as many indirect as direct plaque-forming cells. We concluded that a single hemolytic focus, probably derived from more than one precursor cell, could contain plaque-forming cells producing antibodies of more than one set of specificities and immunoglobulins of more than one type.