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Why do the number of eosinophils decrease? What are the potential reasons?
In the human immune system, eosinophils are an important type of white blood cells. When the number of these cells drops below normal, the phenomenon is called eosinopenia. This condition may be associated with a variety of disease states or physiological changes, causing intense concern among medical professionals. This article will explore the potential causes of decreased eosinophil counts and their possible health effects.
Eosinophils are generally thought to play an important role in fighting allergies and parasitic infections, but their role in other pathologies continues to be studied.
Definition and diagnosis of eosinophilia
In clinical practice, the definition of eosinophilia may vary, but it is generally considered to be hypopenia if the number of eosinophils per microliter of blood is less than 50 cells. Some medical institutions define 10 or less cells as abnormal, and some laboratories even regard 0 cells as within the normal range. Diagnosing eosinophilia can be challenging because there are usually low numbers of eosinophils in the blood, and their numbers can change over time.
Potential causes of eosinophilia
The influence of endogenous tyrosine substances
Research has shown that, unlike other granulocytes, the number of eosinophils decreases after the release of endogenous tyrosine substances. When the body releases substances such as epinephrine, it may affect the production of eosinophils in the bone marrow, causing a decrease in the number in the blood. Specifically, epinephrine appears to affect eosinophil numbers through the beta-adrenergic pathway.
Steroid use
Steroids are known to affect several blood components, including reducing the number of eosinophilic white blood cells. The reasons for this effect are multifactorial: steroids encourage these cells to leave the bloodstream and enter tissues, reducing their numbers in the blood. In addition, steroids inhibit the release of eosinophils from the bone marrow, and it is theorized that apoptosis of these cells in the blood may also be responsible for the reduction in their numbers.
Eosinophil-depleting drugs
Many drugs that target eosinophils are used to alleviate diseases mediated by these cells. These drugs include mepolizumab, reslizumab and benralizumab, which are designed to reduce the number of eosinophils in order to improve patients' symptoms.
Role in inflammation and sepsis
Eosinophils play an indispensable role in the process of inflammation and infection, but the specific mechanism of their reduction remains unclear. Some people believe that the decrease in eosinophils may be a manifestation of an immune system disorder. When faced with a pathogen, the immune system typically launches what is called "type 1 inflammation," which mobilizes specialized immune cells to clear the pathogen. However, this in turn may cause additional damage to host tissue, so eosinophils may help repair damaged tissue as part of "type 2 inflammation."
Persistent eosinophilia may be associated with worse clinical outcomes in sepsis, including higher rates of mortality and hospital readmissions.
Performance in COVID-19
The latest research finds that eosinophilia may also be related to the course of COVID-19. Studies have shown that among hospitalized patients, 53% showed eosinophilia, and in some death cases, this number even rose to 81%. This suggests that the decrease in eosinophils may be related to the severity of the disease in patients, but it is unclear whether it directly affects the course of the disease.
Conclusion
The decrease in the number of eosinophils may have many causes, including endogenous substances, steroid use, and certain drug treatments. This phenomenon may not only be associated with a variety of health conditions, but may also play an important role in the development of sepsis and COVID-19. Therefore, future studies will be devoted to uncovering the specific mechanisms of eosinophilia and its potential impact in various diseases. Faced with these challenges, can we find more effective ways to manage and treat eosinophilia?
