Characterization of Harderian Gland‐Derived Plasma Cells in Chicken

Due to fundamental differences in B cell development between birds and mammals, knowledge of avian plasma cells (PCs) remains scarce, and PC‐specific markers have been lacking. We isolated leukocytes from the Harderian gland (HG), a lacrimal gland rich in PC‐like cells, and identified a subset of large CD45 med cells. Plasma cell identity was confirmed by low Pax5, high Blimp‐1 expression, and characteristic morphology. These cells lacked B lineage marker chB6 but expressed surface BCRs, with a predominant class switch toward IgA and a small fraction of IgY pos cells. Expression of activation marker CD57 and cycling cells indicate incomplete terminal differentiation. The CXCR4 high PCs localized to CXCL12‐rich HG‐areas, supporting conservation of the CXCL12–CXCR4 axis for PC‐migration and retention. HG PCs exhibited a switch from BAFF‐R to TACI expression, suggesting BAFF–TACI signaling may compensate for the absence of BCMA/APRIL in chickens and mediate PC survival. High levels of IL‐6, BAFF, and CXCL12 in HG tissue further indicate the presence of survival niches. This study establishes a method to isolate chicken PCs, defines their phenotype as FSC high /CD45 med /sIg pos /CD57 pos /CXCR4 high /TACI low , and reveals conserved and species‐specific aspects of mucosal PC biology, providing a foundation for functional studies and improved poultry vaccine strategies.