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.