Human monocyte chemotaxis: migrating cells are a subpopulation with multiple chemotaxin specificities on each cell

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Abstract
Only 20-40% of human blood monocytes were monocytes were capable of responding to chemotaxins in vitro. This limit is not due to restrictions of the in vitro system, but is due to the existence of a migrating subpopulation. Over a wide range, the number of cells migrating toward a given concentration of chemotaxin was directly proportional to the number added to the chemotaxis chamber. These monocytes responded to all of the 3 stimuli used: human serum-derived C5a [a fragment of complement component 5], human lymphocyte-derived chemotactic factor and a synthetic peptide. It was possible to deactivate cells to 1 attractant, leaving the response to other attractants intact. These attractants were thus recognized by different receptors. Several lines of evidence showed that most migrating cells had receptors for all 3 chemotaxins tested. If cells were assayed for migration to 1 attractant, no additional migration occurred when the remaining cells were assayed for migration to a different attractant. The same cells that migrated toward 1 attractant were able to respond to other chemotaxins. A single attractant attracted as many cells as a combination of 2 or 3 attractants. Calculations from these data showed that at least 75% of the migrating monocytes have different receptors for all 3 attractants.