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. M-shaped tetramer of two CD180-LY86 heterodimers. Associated with CD180 at the cell surface. Highly expressed in spleen, liver, brain and thymus, and at lower levels in kidney.