Reticulocyte-based estimation of red blood cell lifespan.

We introduce a new, minimally invasive laboratory technique called reticulocyte-based estimation of lifespan (REBEL) of erythrocytes in humans. Its major advantage over existing techniques is its applicability to patients with both changing and steady-state erythropoiesis status. The feasibility of REBEL was tested in five patients with hemodialysis-dependent end-stage renal disease. The RNA degradation half-life was first determined for each subject on day 1 by flow cytometry measurement of the decay rate of thiazole orange stain. Reticulocyte age distribution was then measured from residual RNA content weekly for 2 months to estimate the RBC production rate time course. Mean RBC lifespan per subject was estimated by fitting the integrated RBC production rate over time to the measured RBC count and optimizing the integration limits. The mean reticulocyte RNA half-life was 0.71 ± 0.11 days. The small coefficient of variation (15.6%) indicated that the degradation rate of RNA did not vary substantially between subjects. The mean RBC lifespan (TRBC = 76.6 ± 23.8 days) was comparable to the reported values for this patient population.

Exocytosis of neutrophil granule subsets and activation of prolyl isomerase 1 are required for respiratory burst priming.

This study tested the hypothesis that priming the neutrophil respiratory burst requires both granule exocytosis and activation of the prolyl isomerase Pin1. Fusion proteins containing the TAT cell permeability sequence and either the SNARE domain of syntaxin-4 or the N-terminal SNARE domain of SNAP-23 were used to examine the role of granule subsets in TNF-mediated respiratory burst priming using human neutrophils. Concentration-inhibition curves for exocytosis of individual granule subsets and for priming of fMLF-stimulated superoxide release and phagocytosis-stimulated H2O2 production were generated. Maximal inhibition of priming ranged from 72 to 88%. Linear regression lines for inhibition of priming versus inhibition of exocytosis did not differ from the line of identity for secretory vesicles and gelatinase granules, while the slopes or the y-intercepts were different from the line of identity for specific and azurophilic granules. Inhibition of Pin1 reduced priming by 56%, while exocytosis of secretory vesicles and specific granules was not affected. These findings indicate that exocytosis of secretory vesicles and gelatinase granules and activation of Pin1 are independent events required for TNF-mediated priming of neutrophil respiratory burst.