Arg-Gly-Asp-dependent occupancy of GPIIb/IIIa by applaggin: evidence for internalization and cycling of a platelet integrin

Using indirect immunofluorescence microscopy we examined the distribution and cycling of GPIIb/IIIa after binding to applaggin, a high-affinity Arg-Gly-Asp (RGD)--containing ligand. Resting, unfixed platelets were incubated with applaggin for 30 minutes at 37 degrees C, and bound applaggin was detected by an affinity-purified rabbit anti- applaggin antibody. Examination of intact cells showed a rim pattern for applaggin, consistent with its binding to the platelet surface. Staining of Triton X-100--permeabilized cells showed an intracellular pool of applaggin. Competition of applaggin binding by either AP-2, an anti-GPIIb/IIIa monoclonal antibody (MoAb) that blocks fibrinogen binding, or the synthetic peptide RGDW eliminated both surface and intracellular staining, indicating that applaggin is binding to GPIIb/IIIa in an RGD-dependent manner. Inhibition of platelet activation by PGE1 and theophylline had no effect on the observed staining patterns, indicating that cellular activation is not required for surface binding and subsequent internalization. To evaluate whether occupancy of functional binding sites on GPIIb/IIIa is required for internalization, we used mAb15, an anti-GPIIIa antibody that neither blocks fibrinogen binding nor induces the expression of ligand-induced binding sites on GPIIb/IIIa. In these studies mAb15 was internalized in a manner analogous to both AP-2 and applaggin, showing that occupancy of the RGD binding site is not required to initiate receptor internalization. To estimate the size of the newly internalized pool of applaggin, 125I-applaggin--binding studies were performed. Displacement of bound 125I-applaggin by excess unlabeled applaggin or EDTA showed that at least 17% of bound applaggin was nondisplaceable when binding was performed under conditions permitting membrane flow and internalization. These data indicate that GPIIb/IIIa is internalized in unstimulated platelets independent of cellular activation or occupancy of the functional binding site(s) of GPIIb/IIIa by RGD-containing ligands. Thus, internalization of GPIIb/IIIa may represent a mechanism by which the surface expression of this adhesion receptor is regulated.     

CD34 expression is regulated reciprocally with adhesion molecules in vascular endothelial cells in vitro

Freshly cultured vascular endothelial cells express the CD34 antigen in a diffuse cell surface pattern with some concentration on microvilli. Expression is downregulated with proliferation in continuous culture and undetectable after nine population doublings but can be maintained by restraining cell proliferation and promoting cell contact. Expression of CD34 at the antigen and mRNA levels on early passage cells is rapidly downregulated by interleukin-1 beta (IL-1 beta), interferon-gamma (INF-gamma), and tumor necrosis factor-alpha (TNF- alpha) under conditions in which these ligands upregulate the adhesion molecules: endothelial leukocyte adhesion molecule 1 (ELAM-1) and intracellular adhesion molecule 1 (ICAM-1). This reciprocal pattern of expression and the topographic distribution of CD34 molecules on the lumenal interdigitated microprocesses of adjacent endothelial cells in vivo suggest that CD34 might have a negative modulating role on adhesion functions of endothelia.     

Chronic asymptomatic pseudocyst with sludge aggregates masquerading as mucinous cystic neoplasm of the pancreas

Pseudocyst of the pancreas is sometimes difficult to distinguish from mucinous cystic neoplasm of the pancreas. A 37-year-old asymptomatic Japanese man was diagnosed with hypertension. He had a 20-years history of habitual drinking of alcohol, but no history of pancreatitis or abdominal trauma. During examinations to ascertain the cause of hypertension, ultrasonography and computed tomography incidentally demonstrated a huge cyst in the head of the pancreas. Laboratory data were within normal limits, including serum levels of amylase, carcinoembryonic antigen, and carbohydrate antigen 19-9. Imaging studies showed a huge unilocular cyst, measuring 7 cm, in the head-to-body of the pancreas, and two small unilocular cysts, measuring 1.4 and 1.5 cm, in the tail and head of the pancreas, respectively. A mural nodule was suspected in the largest cyst. Endoscopic retrograde cholangiopancreatography demonstrated communication of the main pancreatic duct with the two small cysts in the head and tail of the pancreas but not with the huge cyst. There were no ductal changes suggesting chronic pancreatitis. Laparotomy was performed under the tentative diagnosis of potentially malignant mucinous cystic neoplasms of the pancreas. However, inflammatory adhesion was dense around the pancreas and the mural nodule suspected preoperatively was found to be sludge aggregates in a pseudocyst. The diagnosis of an intraoperative frozen section of the cyst wall was pseudocyst of the pancreas. Cystojejunostomy was performed. We report this case because the pre-operative diagnosis was mucinous cystic neoplasm of the pancreas, but the diagnosis changed with careful intraoperative examinations, to pseudocyst of the pancreas. We discuss the differential diagnosis of the two conditions. (Received Oct. 1, 1997; accepted Jan. 23, 1998)     

Percutaneous biliary drainage: complications of 118 consecutive catheterizations

We have reviewed our experience with 118 biliary catheterization procedures in 109 patients from 1979 to 1984. Major complications (septic shock, hemorrhage, subphrenic abscess, and formation of an arteriovenous fistula) occurred in five patients (4.2%), three of whom died (2.5%). Minor complications occurred in 41 patients. Our success rate using the procedure was 97%. The complications that occurred are described.