Prevalence of intrinsic factor antibodies and vitamin B12 malabsorption in older patients admitted to a rehabilitation hospital.

It is possible that the commonly measured serum level of vitamin B12 may miss some cases when used to detect vitamin B12 malabsorption and deficiency in older persons. Serum levels of vitamin B12 and intrinsic factor antibody (IFAB) were determined on 250 consecutive patients over the age of 70 admitted to a rehabilitation hospital. Patients with abnormal results on either test were given the standard Schilling test when possible. Eight patients had documented B12 malabsorption. Of these, five had a low serum B12 level alone and one had a low serum B12 level and a positive IFAB level; however, two patients had positive IFAB and normal serum B12 levels. Serum IFAB level may serve as a useful adjunct to serum B12 level in detecting vitamin B12 malabsorption in older patients.

Procoagulant activity associated with plasma membrane vesicles shed by cultured tumor cells.

Thirteen of 14 tumor cells or tumor cell lines of guinea pig, mouse, and human origin spontaneously shed procoagulant activity in short-term (4 or 14 to 22 hr) tissue culture under conditions of high cell viability. This released procoagulant activity was pelletable in the ultracentrifuge and was associated with plasma membrane-derived vesicles as determined by transmission electron microscopy and marker enzyme analysis. The procoagulant activity shed corresponded to a substantial fraction of that expressed by intact or sonicated tumor cells and was composed of activities interacting at more than a single step in the clotting sequence. One procoagulant activity associated with shed human tumor vesicles behaved as tissue factor, requiring Factor VII for activity and being inhibited by a specific anti-bovine tissue factor antibody. Guinea pig tumor vesicles also exhibited tissue factor-like activity in a two-stage assay using homologous first-stage Factor VII/X concentrate. None of the human vesicles tested expressed a direct Factor X cleaving activity, independent of Factor VII. Shed tumor vesicles also acted at a second step late in the clotting cascade at the level of prothrombinase generation, presumably by providing a phospholipid surface. Taken together, these data indicate that a wide variety of tumor cells release plasma membrane vesicles with procoagulant activity. Such vesicles, as well as intact tumor cells themselves, may play an important role in the biology of tumor growth by inducing the local fibrin deposits found in association with many solid tumors.

Tumor shedding and coagulation.

Three syngeneic carcinomas from two species shed plasma membrane vesicles when cultured in vitro or grown in the ascites tumor form in vivo. Shed vesicles carry procoagulant activity that can account for the activation of the clotting system and the fibrin deposition associated with these and many other types of malignancy in animals and man.