In vivo response to IL-6. Four sex- and age-matched mice of each genotype were injected subcutaneously with murine rIL-6 (20 μg/kg) for 5 days. Complete blood counts and 300-count manual leukocyte differentials were performed before the first injection and 4 hours after the last injection of IL-6. The fold change from baseline in the absolute level of circulating neutrophils and lymphocytes is shown. Data represent the mean ± SD.