THE ORIGIN AND SEQUENCE OF THE CELLS FOUND IN THE ACUTE INFLAMMATORY RESPONSE

Summary Experiments were designed to investigate first the origin of the mononuclear cells in inflamed areas, and secondly, the cellular sequence in the acute inflammatory response. It was found that, following several injections of a carbon suspension intravenously into rats, 7–10% of the blood mononuclear cells were labelled with carbon particles. A similar level of labelling was found in exudate mononuclear cells on “skin‐windows” applied to skin surface abrasions, except for a much higher level on those “skin‐windows” applied soon after the last dose of carbon; further experiments indicated that this latter result was a form of artefact due to the ingestion by these cells of carbon particles from labelled polymorphs which had died and disintegrated on the coverslips. In a second series of experiments abrasions made on the skin of rabbits were covered with a “window‐box” chamber containing fluid which was changed and examined at certain intervals. It was found that, although polymorph emigration into the fluid of the chamber reached its peak less than 6 hr. after initiation of an injury, no mononuclear cells were found in the exudates until 8 hr., and then only in very small numbers; the mononuclear cell counts in the fluid did not reach a peak until approximately 24 hr. later. The results of the “skin‐window” experiments indicate that the mononuclear cells found in inflammatory exudates are of haematogenous origin; the results of the “window‐box” experiments confirm that, following injury, there is an early but transient emigration of polymorphs into the acute inflammatory exudate followed by a delayed but more prolonged escape of mononuclear cells.