Localization of the guinea pig eosinophil major basic protein to the core of the granule

Abstract

The localization of the guinea pig eosinophil major basic protein (MBP) within the cell was investigated by the use of immunoelectron microscopy and by isolation of the granule crystalloids. By immunoperoxidase electron microscopy, the MBP of eosinophil granules was shown to be contained within the crystalloid core of the granule. Specific staining of cores was present when rabbit antiserum to MBP was used as the 1st stage antibody in a double antibody staining procedure: staining was not seen when normal rabbit serum was used as the 1st stage antibody. Crystalloids were isolated from eosinophil granules by disruption in 0.1% Triton X-100 and centrifugation through a cushion of 50% sucrose. Highly purified core preparations yielded essentially a single band when analyzed by electrophoresis on polyacrylamide gels containing 1% sodium dodecyl sulfate (SDS). The .**GRAPHIC**. of the core protein was 26.8 .+-. 1.0 (.hivin.X .+-. SEM). The .**GRAPHIC**. for the MBP was 26.3. The core protein could not be distinguished from the MBP by radioimmunoassay (RIA) and essentially all of the protein in the core preparations could be accounted for as MBP. The MBP is apparently contained in the core of the guinea pig eosinophil granule and is probably the only protein present in the core.