Abstract
Eosinophils are granulocytes primarily associated with TH2 responses to parasites or immune hyper-reactive states, such as asthma, allergies, or eosinophilic esophagitis. However, it does not make sense from an evolutionary standpoint to maintain a cell type that is only specific for parasitic infections and that otherwise is somehow harmful to the host. In recent years, there has been a shift in the perception of these cells. Eosinophils have recently been recognized as regulators of immune homeostasis and suppressors of over-reactive pro-inflammatory responses by secreting specific molecules that dampen the immune response. Their role during parasitic infections has been well investigated, and their versatility during immune responses to helminths includes antigen presentation as well as modulation of T cell responses. Although it is known that eosinophils can present antigens during viral infections, there are still many mechanistic aspects of the involvement of eosinophils during viral infections that remain to be elucidated. However, are eosinophils able to respond to bacterial infections? Recent literature indicates that Helicobacter pylori triggers TH2 responses mediated by eosinophils; this promotes anti-inflammatory responses that might be involved in the long-term persistent infection caused by this pathogen. Apparently and on the contrary, in the respiratory tract, eosinophils promote TH17 pro-inflammatory responses during Bordetella bronchiseptica infection, and they are, in fact, critical for early clearance of bacteria from the respiratory tract. However, eosinophils are also intertwined with microbiota, and up to now, it is not clear if microbiota regulates eosinophils or vice versa, or how this connection influences immune responses. In this review, we highlight the current knowledge of eosinophils as regulators of pro and anti-inflammatory responses in the context of both infection and naïve conditions. We propose questions and future directions that might open novel research avenues in the future.
Highlights
Eosinophils are granulocytes primarily associated with TH 2 responses to parasites or immune hyper-reactive states, such as asthma, allergies, or eosinophilic esophagitis
This review aims to gather what is known about eosinophils and their cross-signals with bacteria in the context of infection and microbiota
This possess the question as to what the specific roles of eosinophils are under these conditions: are they participating in the immune responses to bacterial infections? Or do bacterial infections manipulate eosinophils to cause a hyper-reactive state that leads to eosinophilic disorders? In this context, a key area of investigation that has not been fully explored is respiratory diseases and eosinophilic disorders
Summary
The body’s most powerful defense against external insults is the immune system. Orchestration of the intricate web of signals necessary to mount an adequate response to such insults requires finely-tuned mechanisms that mediate the function and activation of different immune cells [1]. Their dense granules contain cationic proteins, which include the major basic protein (MBP), eosinophil peroxidase (EPX), eosinophil cationic protein (ECP), and the eosinophil derived neurotoxin (EDN) [6,7,8] The versatility of these granulocytes in homeostasis and immunity is gradually becoming better understood [9]. Despite being primarily associated with TH 2 responses, eosinophils are known to play a role in the clearance of viral respiratory infections during which they trigger TH 1 immune responses [20,21] This apparent dichotomy only reveals the lack of understanding of the actual role of these cells, as well as their biological functions during immune responses and pathological states. We discuss the mechanisms by which they modulate T cell responses and conclude with perspectives and future directions that would highlight the gaps in the knowledge in this area of investigation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
