THE BACTERICIDAL PERMEABILITY-INCREASING PROTEIN (BPI) IS PRESENT IN SPECIFIC GRANULES OF HUMAN EOSINOPHILS/

Eosinophils participate in the inflammatory response seen in allergy a nd parasitic infestation, but a role in host defense against bacterial infection is not settled. The bactericidal/permeability-increasing pr otein (BPI) has been demonstrated in neutrophils and it exerts bacteri ostatic and bactericidal effects against a wide variety of Gram-negati ve bacterial species. Using the Western blot technique, a 55-kD band, corresponding to BPI, was detected in lysates from both neutrophils an d eosinophils. The localization of BPI in immature and mature eosinoph ils was investigated using immunoelectron microscopy. BPI was found in immature and mature specific granules of eosinophils and was detected in phagosomes as well, indicating release of the protein from the gra nules into the phagosomes. Using a specific enzyme-linked immunosorben t assay, eosinophils were shown to contain 179 ng of BPI/5 x 10(6) eos inophils compared with 710 ng BPI/5 x 10(6) neutrophils. The presence of BPI in eosinophils suggests a role for these cells in host defense against Gram-negative bacterial invasion or may suggest a role for BPI against parasitic infestation. (C) 1998 by The American Society of He matology.