A computer model simulating granulopoiesis has been constructed on the basis of two feedback loops, one controlling the rate of production of granulocytes at the stem cell level, the other controlling the rate of release of granulocytes into the blood. This model reproduced the low-amplitude neutrophil oscillation reported in normal individuals and, when mild and severe marrow failure were simulated, resulted in states resembling cyclical and severe noncyclical neutropenia, respectively. The results provide evidence that a number of the periodic features shown by normal and abnormal granulopoiesis occur because granulopoiesis is a feedback-controlled system and suggest that the main assumptions of the model have physical reality.

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