Eosinophils regulate peripheral B cell numbers in both mice and humans.

Area of Science:

• Immunology
• Cell Biology

Background:

• Eosinophils (Eos) were traditionally viewed as effector cells in host defense and allergic diseases.
• Recent findings suggest Eos interact with both innate and adaptive immunity components.
• Previous research showed mouse Eos promote plasma cell retention in bone marrow.

Purpose of the Study:

• To investigate the influence of eosinophils on normal B lymphocyte biology.
• To assess the specific effects of Eos on B cell survival, proliferation, and immunoglobulin (Ig) secretion.

Main Methods:

• Genetic deletion of Eos in IL-5 transgenic mice to observe effects on B cell lymphocytosis.
• In vitro studies using human tissues to examine Eos-B cell interactions.
• Retrospective clinical analysis correlating peripheral blood eosinophil levels with B cell numbers.

Main Results:

• Genetic deletion of Eos in hypereosinophilic mice nearly abolished B cell lymphocytosis.
• In vitro studies demonstrated Eos promote B cell survival, proliferation, and Ig secretion via contact-independent mechanisms.
• Eos enhance B cell responsiveness in both T-independent and T-dependent activation, irrespective of Eos activation state.
• A clinical study showed a correlation between peripheral eosinophil counts and B cell numbers.

Conclusions:

• Eosinophils play a novel role in regulating humoral immunity.
• Eos impact B cell homeostasis and proliferation upon activation.
• This study redefines the role of eosinophils beyond effector functions.