RELATIONSHIP OF THE WHITE BLOOD-CELL COUNT TO BODY-FAT - ROLE OF LEPTIN

The white blood cell (WBC) count is correlated to the amount of body f at in humans, but the mechanism for this association is unknown, Lepti n, a 16 kD protein produced in adipocytes, circulates in humans in dir ect proportion to the amount and percentage of body fat. Recent eviden ce suggests that leptin and the leptin receptor are part of a novel pa thway which stimulates haemopoiesis. This study was designed to test w hether fasting plasma leptin concentrations contribute to the relation ship between the WBC count and body fat. 117 Pima Indians with a wide range in body composition were studied. The WBC count was positively c orrelated with percentage of body fat (r = 0.44, P = 0.0001) and fasti ng plasma leptin concentration (r = 0.38. P = 0.0001). In multiple reg ression analyses, age, gender and percent body fat were significant in dependent determinants of the WBC count. After controlling for age and gender, percent body fat accounted for 23% of the variance in the WBC count (partial r = 0.48, P = 0.0001). In similar models which also in cluded plasma leptin concentration, percent body fat remained signific antly related to the WBC count, but only accounted for 7% of its varia nce (partial r = 0.27, P = 0.003). Based on these results, and the dem onstration that leptin directly effects the stimulation of proliferati on of haemopoietic stem cells in vitro, we hypothesize that the relati on of the WBC count to percent body fat may be mediated, in part, thro ugh the effect of leptin.