Down-regulation and inactivation of neutral endopeptidase 24.11 (enkephalinase) in human neutrophils.

Neutral endopeptidase (EC 3.4.24.11, NEP) is an integral membrane protein of human neutrophils. NEP is identical with the common acute lymphoblastic leukemia antigen (CALLA) of leukemic cells. The expression of NEP on the surface of neutrophils is down-regulated by endocytosis which can be induced by phorbol 12-myristate 13-acetate (PMA) at 37 degrees C. The activity of the enzyme on the surface of intact cells decreases by 76% within 5 min. The activity can be recovered, however, if the cells are lysed within 5 min of the endocytosis. After 30 min, only 32% of the NEP activity is present in the neutrophil lysates. The loss of activity is presumably due to proteolytic inactivation. Diacylglycerol and monoclonal antibody to CALLA/NEP also induce internalization of NEP. PMA induces endocytosis even at 4 degrees C, but NEP is not inactivated at that temperature. The disappearance of NEP activity after adding PMA was inhibited by various agents. Among the most active were the phospholipase inhibitor 4-bromophenacyl bromide and a combination of the serine protease and cathepsin inhibitors, diisopropylfluorophosphate and N-ethylmaleimide. The employment of fluorescent monoclonal antibody confirmed the down-regulation and internalization of NEP antigen on the neutrophils. Since NEP inactivates chemotactic peptides and thereby affects chemotaxis of neutrophils (Painter, R. G., Dukes, R., Sullivan, J., Carter, R., Erdös, E. G., and Johnson, A. R. (1988) J. Biol. Chem. 263, 9456-9461), the down-regulation of NEP activity on the cell membrane may modulate the function of these cells in inflammation.

The effect of delayed refrigeration on red blood cells, platelet concentrates and cryoprecipitable AHF.

The effect of delaying blood processing for six hours while maintaining it at ambient temperature was investigated. Blood drawn from volunteers on two occasions was processed immediately (I) or after a six-hour delay (D). The effects of the delay on the efficacy and safety of red blood cells, platelet concentrates and cryoprecipitable AHF were studied. There was a more rapid decrease in 2,3-DPG in the delayed group during 21 days of refrigerated storage. ATP levels declined at similar rates. 24-hour survival of 51CR-labeled autologous cells was slightly better (p = .05) in the (I) group but excellent for both. Total platelets, per cent recovery and pH at 72 hours were identical for both groups. All cultures were sterile. There was no difference in total AHF recovered or per cent recovery between the two groups. To increase the availability of blood components, a six-hour processing delay seems warranted.

A physiological sealant for cerebrospinal fluid leaks.

A combination of concentrated platelets, thrombin, and fibronogen was used to adhere a pericranial graft to surgically produced cerebrospinal fuild (CSF) fistulas in dogs. This sealant successfully stopped leakage of CSF in all fistulas produced in both acute and chronic preparations. All control animals leaked CSF acutely. In chronic control animals the CSF leaks sealed spontaneously but the grafts were not well incorporated. Histoligical examination of the grafts and underlying brain showed not injury to the brain of meningeal vessel from exposure to the platelet glue. Good fibrous union of the grafts to the dura was confirmed.