Concanavalin A-induced Macrophage Aggregating Factor

The production of the lymphokine activity macrophage aggregating factor (MAgF) by Concanavalin A (Con A)-pulsed guinea-pig spleen cells has been investigated. The following observations have been made: (1) MAgF can be assayed quantitatively by measuring the light absorbance of peritoneal exudate cells (PEC) using a spectrophotometer, rather than the previously used Born platelet aggregometer; (2) both Con A and antigen-induced MAgF elute from Sephadex G-200 over the 30,000-70,000 m wt range; (3) Con A-pulsed spleen cells generate supernatants which can be assayed directly for MAgF. Inhibitor studies with alpha-methyl-D-mannoside show that the observed PEC aggregation is due to MAgF and not to residual Con A, which also aggregates these cells.