Life Cycle of Granulocytes and Lymphocytes Determined by Making Use of ⁵⁹Fe Labelled Haemin as a Tracer

Summary. In granulocytes and lymphocytes separated from the blood of the rabbit the incorporation of radioactive 59 Fe into the haemin fraction was investigated. Evidence is presented that the iron is incorporated into the haemins during the formation of these cells and remains in them during their life time. From the change of the specific activity of the haemin iron with time the average life span of both lymphocytes and granulocytes can thus be calculated. The mean age of the granulocytes was found to be 8.8 days. It is presumably composed of two populations of about the same frequency but varying life time, one having a life span of 4.4, the other of 13.2 days. The mean age of 8.8 days is identical with the result obtained by O ttesen from 32 P data of DNA isolated from granulocytes. A very appreciable part of lymphocytes has a life span amounting to 145 days; 10 % only having one of 3 days. An almost identical result was arrived at by O ttesen in his DNA studies. A part of the lymphocytes entering the blood stream is still going on to incorporate haemin iron, thus to build up haemin.