A B lymphocyte mitogen extracted from a fungus Peziza vesiculosa.

A water-soluble mitogen was extracted with hot-water from the fruiting bodies of a fungus, Peziza vesiculosa, collected in the wild. The active substance, named vesiculogen, was able to stimulate selectively murine B cells because mitogenic activity was observed in the spleen cell cultures of congenitally athymic nude mice, but not in the thymus cell cultures. The possibility that the mitogenicity of vesiculogen was due to lipopolysaccharide was denied completely by the following evidence: 1) lipopolysaccharide in vesiculogen was undetectable(less than 0.001% in the Limulus test), 2) vesiculogen was able to stimulate strongly DNA synthesis of spleen cells from C3H/HeJ mice, and 3) the mitogenic activity of vesiculogen was not inhibited by polymyxin B. Vesiculogen increased antigen-nonspecifically the number of direct plaque forming cells to sheep erythrocytes, horse erythrocytes, and trinitrophenylated-horse erythrocytes. This result shows that vesiculogen acts as a polyclonal B cell activator on murine spleen cells.