Carrageenan-mediated suppression or augmentation of mitogen-induced lymphocyte proliferation.

The effects of carrageenan on mitogen-induced lymphocyte proliferation were studied in the guinea pig. According to the dose used, carrageenan displayed opposite effects on thymidine uptake by spleen cells or peripheral blood leukocytes stimulated by Concanavalin A or phytohemagglutinin (25 micrograms ml-1 carrageenan increased whereas 0.25 microgram ml-1 depressed thymidine incorporation). Carrageenan, at the high concentration which increased thymidine uptake by mitogen-stimulated spleen cells, potentiated the enhancing activity of macrophages that was observed with cell suspensions containing 20% macrophages. Conversely, low concentrations of carrageenan abolished the enhancing effect of macrophages. These effects of carrageenan on lymphocyte proliferation could be explained by its activities on a macrophage functional subset rather than on the whole macrophage population.