May be involved in B-cell development and differentiation in peripheral lymphoid organs and may be useful markers of B-cell stages. May have an immunoregulatory role in marginal zone B-cells. Expressed in marginal zone B-cells, immunoblasts, tonsillar germinal center centrocytes and in the intraepithelial and interfollicular regions of the tonsil. Expressed in many lymphoma cell lines and on hairy cell leukemia cells. Isoform 1, isoform 3, isoform 4 and isoform 5 are detected in lymph node, spleen, bone marrow, and small intestine with preponderance of isoform 3. Expressed in mature and memory B-cells and down-regulated in germinal center cells (at protein level). Contains 2 copies of a cytoplasmic motif that is referred to as the immunoreceptor tyrosine-based inhibitor motif (ITIM). A chromosomal aberration involving FCRL5 has been found in cell lines with 1q21 abnormalities derived from Burkitt lymphoma. Duplication dup(1)(q21q32).