SPECIFIC HETEROLOGOUS ENHANCEMENT OF IMMUNE RESPONSES : IV. SPECIFIC GENERATION OF A THYMUS-DERIVED ENHANCING FACTOR

In short-term cultures of thymocytes from tetanus toxoid-immunized mice, the addition of 1 ng of toxoid generated the release of a soluble factor which was capable of enhancing the immune response to a heterologous immunogen. The addition of supernatants from such cultures to assay cultures of sheep erythrocyte-stimulated normal spleen cells produced a significant augmentation of the hemolytic plaque response. Culture fluid from similar cultures of normal thymocytes or primed thymocytes cultured without the priming antigen were inactive. The enhancing factor was nondialyzable, heat stable (56°C, 30 min), resistant to DNAse and RNAse, but was inactivated by protease. A factor produced by specifically stimulated primed spleen cells had similar characteristics. In toxoid-stimulated, mixed cell cultures containing primed thymocytes or spleen cells and normal spleen cells, tenfold fewer thymocytes than spleen cells were needed to produce a comparable degree of enhancement of the anti-sheep erythrocyte plaque-forming cell response

STUDIES ON MEMBRANE-BOUND RECEPTORS FOR ANTIGEN : PREPARATION OF POPULATIONS OF RECEPTOR-DEPLETED LYMPHOCYTES

The effect of polyadenylic: polyundylic acid complexes (poly A:U) on the amount of antibody on the surface of various populations of mouse lymphoid cells has been investigated by means of a sensitive measure of such activity—the binding by primed cell populations of β-galactosidase (βGZ) as an antigen. The sensitivity derives from the liberation of fluorescein from an artificial substrate, fluorescein-di-β-galactopyranoside (FDβG). After incubation with 100 ng/ml of poly A:U, only 40% of the cells previously showing antigen-binding were still active. The optimum range of activity lay between 0.01–1.0 µg/ml poly A:U. Such cells showed increased RNA and protein synthesis as indicated by [3H]uridine and [14C]amino acid incorporation. The polynucleotide effect was abolished by incubation of the cells with sodium azide or iodoacetate, but not by puromycin. When the proteins on the cell surface were labeled by 125I, poly A:U caused their release into the medium. Reports by others that the enhancing effect of polynucleotides on the immune response involves the adenylcyclase system are consistent with the finding reported here that reduction of binding by dibutryl 5'-cyclic monophosphoric acid (cAMP) and poly A:U were parallel in extent, and that theophylline and poly A:U acted synergistically in suboptimal concentrations of each