Rat lymphocyte mitogenesis by aggregation factor from rat ascites hepatoma cell surface

Two-tumour-cell-aggregation factors derived from rat ascites hepatoma cells had different antigenicity; one, with a strong potency, was not absorbed by immunoadsorbent chromatography with anti-rat serum antibody and the other, with a weak potency, was. The unabsorbed factor possessed mitogenic activity on lymphocytes from thymus, spleen and lymph node of rats; its effect was compared with that of lectins (including phytohaemagglutinin, concanavalin A, pokeweed mitogen, lipopolysaccharide and soybean agglutinin) in the form of increased DNA and protein synthesis, blast transformation and mitosis. In the use of anti-thymocyte serum-resistant spleen cells and hydrocortisone-resistant thymocytes, the cells stimulated were assumed to be T-lymphocytes. DNA synthesis by this factor seemed to be characterized by a 2-step increase, suggesting the presence of 2 subpopulations of the cells activated, especially thymocytes. At high concentration this factor induced no depression of DNA synthesis. Favourable cell density for the response to this factor was 2-8 X 10(6) cells. Its effect was not influenced by treatment of the cells with neuraminidase.