Formation of total, active and stable E-rosettes by human lymphocytes stimulated with con A derivatives.

Peripheral blood lymphocytes from healthy human volunteers where incubated for 48 hr with 10 micrograms/ml of native Con A or its dimeric derivatives, succinyl- and acetyl-Con A. The percentage of total-active and stable E-rosettes were determined before and after incubation. There were no differences among the three forms of the lectin. Stable E-rosettes exhibited the most dramatic effects from Con A stimulation. They increased from approximately 2% in control cultures to 20-25% in stimulated cultures. Treatment with the Con A inhibitor alpha-Methyl-D-mannoside after Con A stimulation did not affect the rosette formation. Our results suggest that redistribution of membrane receptors on stimulated lymphocytes is not responsible for increased E-rosette formation after Con A stimulation since dimeric forms of Con A are not able to induce membrane receptor redistribution.

Macrophage-agglutinating factor produced in vitro by BCG-sensitized lymphocytes.

Supernatant fluids from cultures of BCG-sensitized rabbit lymph node and spleen cells contained a factor that strongly agglutinated normal rabbit alveolar macrophages within 3 min at room temperature. In contrast, fluids from nonsensitized cell cultures did not agglutinate normal rabbit alveolar macrophages. This factor was designated macrophage-agglutinating factor (MAgF) because it is similar to the previously described factor found in lung lavages of rabbits exhibiting a BCG-induced pulmonary delayed hypersensitivity reaction. The kinetics of MAgF production in vitro by sensitized lymph node cells and its inhibition by puromycin and actinomycin D suggest active synthesis; sensitized spleen cells exhibited kinetics resembling release rather than synthesis. Studies on purified lymphocyte and macrophage populations from sensitized spleen and lymph nodes indicated that lymphocytes are responsible for MAgF production. However, MAgF production was not induced in normal cells incubated in vitro with concanavalin A or phytohemagglutinin. Fractionation of cell culture supernatant fluids in Sephadex G-100 or Ultrogel AcA-34 clearly separated MAgF from migration inhibition factor; MAgF was present in the void volume of the eluates, suggesting a molecular weight of over 400,000, whereas migration inhibition factor was recovered in the same peak as albumin. The role of MAgF in vivo is unknown, but it is postulated that it may cause the adherence of macrophages during granuloma formation.