Glucose-6-phosphate dehydrogenase variants: reexamination of G6PD Chicago and Cornell and a new variant (G6PD Pea Ridge) resembling G6PD Chicago

Two large and unrelated families were investigated for hereditary nonspherocytic hemolytic anemia associated with deficiency of erythrocyte glucose-6-phosphate dehydrogenase (G6PD). In both families, the kinetic and electrophoretic features of the G6PD variants resembled those of G6PD Chicago. Further investigation revealed that members of one of these families previously had been characterized as having the G6PD variants Chicago and Cornell. However, it is clear that each of these terms has been applied to the same variant in this single large kindred. In the second family, we describe a newly identified variant with unique characteristics, which we have designated G6PD Pea Ridge. G6PD Pea Ridge resembles G6PD Chicago but differs in electrophoretic mobility and in a few kinetic parameters. It exhibits an unusually high Ki for NADPH and thus appears to be insensitive to product inhibition. As other cases previously considered to be the Chicago variant become more fully characterized, this probably will be shown to be a heterogeneous group of variants.     

Demonstration of reversible priming of human neutrophils using platelet- activating factor

Exposure of neutrophils to agents such as lipopolysaccharide, tumor necrosis factor-alpha (TNF-alpha), and the granulocyte-macrophage colony-stimulating factor causes a major upregulation of subsequent agonist-induced NADPH oxidase activation. This priming effect is a prerequisite for neutrophil-mediated tissue damage and has been widely considered to be an irreversible process. We have investigated the potential for neutrophils to recover from a priming stimulus by studying the effects of platelet-activating factor (PAF). PAF did not stimulate respiratory burst activity directly, but caused a rapid (maximal at 10 minutes) and concentration-dependent (EC50 50.2 nmol/L) increase in N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated superoxide anion release. At time-points > 10 minutes, this priming effect spontaneously declined, with return to basal levels of fMLP- stimulated superoxide anion generation by 120 minutes. An identical priming time-course was observed with N-methyl carbamyl PAF, a nonmetabolizable analogue of PAF, indicating that the transient nature of PAF-induced priming was not secondary to PAF metabolism. Two structurally diverse PAF receptor antagonists (UK-74,505 and WEB 2086), added 10 minutes after PAF addition, increased the rate of decay of the priming effect. In contrast, TNF-alpha-induced priming, which was of a similar magnitude to that observed for PAF, was slower to evolve (maximal at 30 minutes) and remained constant for at least 120 minutes. The reversible nature of PAF-induced priming was confirmed by demonstrating that PAF-, but not TNF-alpha-, induced cell polarization (shape change) and CD11b-dependent neutrophil binding of albumin-coated latex beads was also transient, with return to basal, unstimulated levels by 120 minutes. Furthermore, cells that had spontaneously deprimed following PAF exposure retained their capacity to be fully reprimed by a subsequent addition of either PAF or TNF-alpha. These data imply that neutrophil priming is not an irreversible event: the demonstration of a cycle of complete priming, depriming, and repriming offers the potential for functional recycling of neutrophils at sites of inflammation.