Isolation of plasma membrane fragments and vesicles from ascites fluid of lymphoma-bearing mice and their possible role in the escape mechanism of tumors from host immune rejection

Summary Plasma membranes, generated in vivo by actively growing YAC lymphoma cells, were isolated from cell-free ascites fluid of lymphoma-bearing mice. Partial purification of the ascites fluid (AF) by means of ultracentrifugation resulted in the identification of two main fractions: (a) membrane fragments (AFM _s ) and (b) membrane vesicles (AFM _p ). Electron microscopy studies, polyacrylamide gel electrophoresis, marker enzymes, and binding capacity of radioactive lectins, have indicated that these membranes are released from the cell surface of YAC lymphoma cells, presumably by a shedding-off mechanism.In vitro studies have demonstrated that the isolated membranes can specifically inhibit the association of normal macrophages and YAC lymphoma cells. In vivo studies have shown that these membranes can immunize against YAC tumors if injected intramuscularly or subcutaneously into adult mice. The results indicate that the ascites fluid membranes bear tumor-specific antigenic determinants.Our results suggest that in vivo shedding of plasma membrane fragments or of membrane vesicles by actively growing YAC lymphoma cells may induce a self-protection of ascites tumors from host immune rejection.Abbreviations YAC= Moloney-virus-induced lymphoma cells grown in A-strain mice - AF= ascites fluid of YAC lymphoma-bearing mice - AFM_s and AFM_p= membrane fragments and vesicles isolated from AF - PBS= phosphate-buffered saline - Con A= Concanavalin A     

Staining Pineal Parenchyma by A Modified Hortega Method After Paraffin Embedding

Fresh pineal glands are fixed in 10% formalin at room temperature for about 3 days. After washing, dehydrating and clearing they are embedded in paraffin, sectioned and mounted. The tissues are placed in 10% silver nitrate for 24 hours, washed and impregnated in strong silver carbonate. The sections are reduced in 10% formalin, washed and toned in gold chloride, fixed in 5% hyposulfite, counterstained with erythrosin and mounted in Canada balsam. The processes of the pineal parenchymatous cells of the sheep, cow and man have been successfully stained by this method.