FCRL4 (Fc receptor like 4) is an immunoregulatory receptor primarily expressed on memory B cells that functions as an inhibitor of B-cell receptor signaling. FCRL4 serves as a bona fide Fc receptor, binding efficiently to IgA antibodies and functioning in immune complex-dependent B cell regulation 1. The receptor is specifically expressed by memory B cells localized in sub-epithelial regions of lymphoid tissues in healthy individuals 2. FCRL4+ B cells represent a distinct memory B cell subset defined by phenotypic markers and display functional heterogeneity, including reduced proliferation and differentiation potential compared to FCRL4- cells 32. These cells strongly express inhibitory receptor genes and demonstrate two-fold lower cell division rates, making them less prone to differentiate into plasma cells 2. Pathologically, FCRL4+ B cells are expanded in various infectious and autoimmune disorders, including Sjögren's syndrome where tissue-resident FCRL4+ B cells produce enhanced pro-inflammatory cytokines and serve as key drivers in patients with MALT-lymphomas 4. In nasopharyngeal carcinoma, CD20+FCRL4+ B cells interact with CD8+ T cells through the MHC-I pathway and correlate positively with PD-1 expression and anti-PD-1 therapy response 5. Decreased FCRL4 expression has been associated with rheumatoid arthritis, suggesting its contribution to inflammatory processes 6.