SPLENIC “POLISHING”: REMOVAL OF HIGH MOLECULAR WEIGHT RED CELL (RBC)MEMBRANE PROTEIN DETRITUS BY THE SPLEEN

To determine whether splenic “polishing” and “pitting” of RBC includes removal of agglomerated membrane proteins as well as membrane lipids and intracellular debris we examined the RBC membrane proteins of normal and splenectomized patients.RBC ghosts were dissolved in sodium dodecyl sulfate (SDS) and chromatographed on Sepharose 2B (exclusion limit=40×106). Membranes from splenectomized patients contained an excluded macromolecular species not present in “normosplenic” individuals. This colorless material formed insoluble fibrils on removal of SDS and was proteinaceous as judged from amino acid analysis and ultraviolet spectroscopy. It comprised 4.2±1.3% (range 2.4-6.1%) of the total membrane protein. Equal proportions were present in membranes from older (more dense) and younger (less dense) cells. When freeze-thawed ghosts were banded on a sucrose density gradient, this material remained with the membrane fraction, indicating it was not a particulars cytoplasmic contaminant. Reduction partially disaggregated the complex and revealed spectrin (a high molecular weight RBC membrane protein thought to be involved in red cell shape maintenance), and at least one other unidentified protein component on SDS-gel electrophoresis.These studies suggest the spleen normally “polishes” or “pits” from RBC membranes an aggregated complex of RBC membrane proteins. Thus RBC membrane proteins join lipids and intracellular particles as targets for splenic cleansing.