May play a role in triggering innate immune responses. Does not seem to play a role for any class I MHC antigen recognition. Expressed mostly in tissues of the hematopoietic system, including bone marrow, spleen, lymph node and peripheral leukocytes. Among leukocytes, monocytes and neutrophils express the highest level. Expressed in CD14+ monocytes, but not in T-cells, B-cells or natural killer (NK) cells (at protein level).