May cooperate with CD180 and TLR4 to mediate the innate immune response to bacterial lipopolysaccharide (LPS) and cytokine production. Important for efficient CD180 cell surface expression (By similarity). M-shaped tetramer of two CD180-LY86 heterodimers. Associated with CD180 at the cell surface. Highly expressed in B-cells, monocytes and tonsil. In monocytes, down-regulated by the cell-wall fraction of Mycobacterium bovis (BCG-CWS).