Selective activation of human eosinophils by bacteria belonging to different taxonomic groups

Abstract

Rationale Eosinophils are found in tissues with an interface with the external environment, such as the gastrointestinal, genitourinary and respiratory tracts. Our hypothesis is that eosinophils can recognize and be activated by microorganisms that enter tissues when mucosal membranes are leaky, i.e. during inflammatory conditions. Methods We tested the capacity of bacteria belonging to different taxonomic groups to mobilize eosinophils and cause the release of the granule proteins major basic protein (MBP), eosinophil cationic protein (ECP) and eosinophil peroxidase (EPO). Blood donor-derived eosinophils were incubated with 11 strains of bacteria. Degranulation was assessed by EIA and intracellular FACS staining. Chemotaxis was tested in a dual chamber microwell system. Results Only certain species of bacteria, both grampositive and gramnegative ones, caused release of ECP and EPO, proteins stored in the matrix of specific granules. In contrast, the majority of tested bacterial species elicited degranulation of MBP, which is found in the core of specific granules. However, eosinophil chemotaxis could only be elicited by a limited number of gramnegative bacterial species. Conclusions Bacterial species are able to cause degranulation of eosinophils. There appears to be a selectivity in the degranulation process, since most bacterial species caused release of MBP, but only certain species were able to elicit release of ECP and EPO and even fewer gave rise to chemotactic behavior.