The Role of Eosinophils in Non-Parasitic Infections

Abstract

Eosinophils are a subset of leukocytes the traditionally associated with Th2-related diseases and helminth infections. However, accumulating evidence suggests that eosinophils play a more prominent role in the immune response to bacterial and viral pathogens than previously realized. Specifically, eosinophils possess antimicrobial properties against a broad range of pathogens, and release specific and secondary granules as a result of pathogen recognition. Pathogen recognition is accomplished through expression of Toll-like receptors, as well as other surface and intracellular receptors expressed by the eosinophil. Interestingly, specific killing mechanisms employed by each granule protein differ based on pathogen recognition, but ultimately release of eosinophil granules leads to direct killing of many different pathogens. The precise mechanisms of killing by granule proteins and the circumstances in which specific proteins are secreted are only now being determined. Future efforts to understand these mechanisms may lead toward clinical use of granule proteins as antimicrobial agents in humans, in addition to revealing implications regarding the use of eosinophil-depleting therapies for allergic disorders. This review will summarize the literature to date regarding the role of eosinophils in non-parasitic infections.

Eosinophils and Neutrophils—Molecular Differences Revealed by Spontaneous Raman, CARS and Fluorescence Microscopy

“…In the spectrum of MPO these bands were shifted, i.e., the Soret band was present at 428 nm, Q v and Q 0 absorbances were found at 499 and 572 nm, respectively, while the CT absorbance was located at 623 nm. An additional band at 687 nm was of unknown origin [ 16 , 38 , 39 ], while the band at 740 nm was again an artefact. The spectral variations can be attributed to the slightly different molecular structures of the porphyrins and surrounding polypeptide chains of these proteins ( Figure 1 A) [ 11 , 19 , 37 ].…”

“…MPO in combination with H 2 O 2 and halides is involved in killing viruses, and bacteria. EPO also shows antibacterial activity but only in the presence of bromides [2,[15][16][17]. In order to differentiate EOS and Ne cells, their peroxidases have been analyzed by employing Raman spectroscopy, in particular resonance Raman spectroscopy.…”

Eosinophils in infection and intestinal immunity

“…While cytotoxic granule proteins are thought to be major contributors to the bactericidal potential of eosinophils, there is evidence that superoxide production via eosinophil-derived NADPH oxidase can also kill bacteria [107]. However, this evidence also suggests that majority of the NADPH-oxidase dependent activity is in conjunction with EPO-hydrogen peroxide-halide bactericidal system [108,107]. …”

Eosinophils—from cradle to grave

“…Eosinophils also play a role in the complex defence against selected bacteria. Although their phagocytic activity and bacterial killing is lower compared with neutrophils, they contribute to the clearance of selected bacteria while their granular proteins and enzymes help to neutralize bacterial proteins 82,83 . Formation of eosinophil extracellular traps (stimulated by several mediators, for example thymic stromal lymphopoietin in humans) is an important phenomenon in bacterial killing 84 .…”