Functional characteristics of monocytes. 1. Essential role in the transformational response of human blood lymphocytes to phytomitogens.

Phagocytic glass-adherent mononuclear cells in peripheral human blood (morphologically monocytes) have been shown to play an essential role in lymphocyte transformational response to phytomitogens. Lymphocytes from peripheral blood have been exhaustively depleted of monocytes by successive treatments, first with opsonized iron particles with eventual magnetic elimination of phagocytic cells, followed by filtration of the same population through packed glass-sand columns. This subpopulation, enriched in T lymphocytes and containing around 4% B lymphocytes, does not transform in response to concanavalin A, phytohemagglutinin, or pokeweek mitogen unless viable monocytes are added to the culture. Supernatant fluids from monocyte-enriched human blood leukocyte cultures can substitute for monocytes in restoring response. Interaction of the phytomitogen with lymphocyte, while essential, is not sufficient to trigger transformation, requiring a second signal provided by the monocyte probably via release of soluble mediators.