FCRLB (Fc receptor-like B) is an intracellular Fc receptor homolog expressed in B cells, particularly within germinal centers 1. As a member of the structurally diverse FcR-like protein family 2, FCRLB functions in immunoglobulin-mediated immune responses and B cell regulation. Mechanistically, FCRLB lacks a transmembrane domain and localizes to the cytoplasm 1, where it may modulate B cell clonal expansion and differentiation 1. FCRLB polymorphisms (rs4657093) are independently associated with IgA nephropathy (IgAN) susceptibility in Chinese populations, with protective genotypes correlating with lower FCRLB expression and improved renal function (serum creatinine, eGFR) 3. In autoimmune myasthenia gravis, FCRLB silencing substantially suppressed anti-MuSK antibody production without eliminating major lymphocyte populations, suggesting selective inhibition of pathogenic B cell responses 4. Conversely, FCRLB appears as a risk factor in multiple cancer types, with high expression associated with poor outcomes in some tumors 5. FCRLB upregulation occurs in severe Mycoplasma pneumoniae pneumonia, correlating with altered immune responses 6. These findings position FCRLB as a potential therapeutic target in antibody-mediated autoimmunity and select malignancies.