Anti-B1 antibodies are used in antigen-specific immunodetection in biological samples. The target B1 is a known alias name of the protein membrane spanning 4-domains A1, encoded by the MS4A1 gene in humans. This 297-amino acid residue protein is known to be involved in B cell differentiation and receptor-mediated signaling pathways, among other biological processes. It is localized to the cell membrane of the cell and features phosphorylated post-translational modifications. In terms of tissue expression, it is noted to be expressed on B-cells.