[1][2] Along with the other granulocytes, eosinophils are part of the innate immune system and contribute to the defense of the body from pathogens.

[3] The opposite phenomenon, in which the number of eosinophils present in the blood is higher than normal, is known as eosinophilia.

[1][4] Eosinopenia is associated with several disease states and conditions, including inflammation and sepsis, endogenous catecholamines, and use of glucocorticoids.

[1] There are also medications that deliberately target eosinophils in order to treat eosinophil-mediated diseases, causing drug-induced eosinopenia.

[1] A hypothesized mechanism contributing to this change is decreased eosinophil production by the bone marrow in response to catecholamines.

Epinephrine is also believed to stimulate receptors through the β-adrenergic pathway to decrease eosinophils in peripheral blood.

Glucocorticoids decrease the number of eosinophils in the circulation by causing them to exit the bloodstream and move into the tissue.

As a result, eosinopenia may be a sign that the body has not mounted an appropriate type 2 inflammation response, so it may be doing more damage than normal to surrounding tissue.

[5] It is unknown if eosinophils contribute directly to clearing pathogens in sepsis or if their absence is only an indicator that the immune system is dysregulated.

[3][8] Though there is early research on the role of eosinophils in response to respiratory viruses, this function is still uncertain and requires additional research in order to define the extent to which eosinophils participate in antiviral immune response as well as clinical relevancy.