Preliminary investigations of eosinophil cationic related protein, a putative eosinophil granule protein.

Eosinophils play a dual role in the hose immune response. Whereas considerable evidence exists that are effective in defending the host against parasite infections, they also play an important role in the inflammatory pathology resulting from parasitic infections and allergic reactions. De-granulation of the eosinophil and release of its cytotoxic proteins are important both in the host defense and inflammation. For example, the granule proteins are toxic to parasites as well as normal host tissue. Eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP) are ribonucleases of the eosinophil granule. We report on studies of a putative novel protein in the eosinophil granules isolated from lysates of human eosinophil granules from a patient with hypereosinophilic syndrome. This putative protein is named Eosinophil Cationic Related Protein (ECRP). We attempted to isolate ECRP from the granule lysates by get filtration and ion exchange chromatography. Chemiluminescent immunodection using polyclonal antibodies revealed a band on western blots which reacted to ECRP antibodies. The sequence homology, conservation of known functional sites, and chromosomal mapping to the same region in chromosome 14 as EDN and ECP strongly suggest that ECRP is also a ribonuclease with functions similar to both ECN and ECP. RCEP has a predicted weight of 14.7KDs and a predicted PI of 9.72. ECRP has 90% identity to EDN in sequence homology. The putative ECRP appears to have an open reading frame that is transcriptional active in response to IL-5. Furthermore, ICRP antibodies reacting to granule lysates suggests that the ECRP protein is likely to be present in eosinophil granules.