Fc Receptor-like 4
Fc Receptor-like 4 (FCRL4) stands out within the Fc receptor-like family for its highly restricted expression on memory B cells resident in mucosal and lymphoid tissues, such as tonsil, rather than in peripheral blood. Like several family members it possesses immunoglobulin-like extracellular domains and ITIM-containing cytoplasmic motifs, and cross-linking studies indicate an inhibitory effect on B-cell receptor signaling. Because FCRL4 marks tissue-homing memory B cells, it has drawn attention in rheumatoid arthritis, where FCRL4-positive B cells accumulate in inflamed synovium, and in chronic infections such as hepatitis C. FCRL4 is therefore a useful marker for dissecting tissue memory B-cell niches.
