TRAP

Synonyms: Tartrate Resistant Acid Phosphatase, Acid phosphatase 5, tartrate resistant (ACP5)

by Jan Klos

Background

TRAP (Tartrate Resistant Acid Phosphatase) is a glycosylated monomeric metalloprotein enzyme encoded on chromosome 19 (19p13.2–13.3). It is synthesized as latent proenzyme and activated by proteolytic cleavage and reduction. It has a critical role in many biological processes including skeletal development, collagen synthesis and degradation, the mineralization of bone, cytokine production by macrophages and dendritic cells, macrophage recruitment, dendritic cell maturation. It is associated with osteoclast migration to bone resorption sites, osteoclast differentiation, activation, and proliferation. Antigen is localized in lysosomes, Golgi system and cytoplasmic vesicles.

Expression in normal cells

Highly expressed by osteoclasts,  activated macrophages, dendritic cells and neurons. The last usually shows lower expression than osteoclasts. Lymphoid cells in marginal zone are positive too.

Expression in tumors and pathological conditions

  • Stains positively both giant and mononuclear cells in 100% giant cells tumors of bone and tendon sheaths, central giant cells granulomas of jaw and peripheral giant cell granuloma in gingiva
  • Positive also in >95% cases of hairy cell leukemia, >90% of splenic and 60-70% extranodal marginal zone lymphoma, 60% of mantle cell lymphoma, 40-50% of DLBCL of mediastinal subtype
  • 40% of B-CLL, 30% of MALT cases, 15% of DLBCL of cutaneous type and 10% of FCL
  • Gaucher’s disease, HIV-induced encephalopathy, osteoclastoma and osteoporosis, and metabolic bone diseases

Staining pattern

Staining pattern is cytoplasmic, often diffuse and/or granular.

Application

  • Sensitive, but not particularly specific marker of hairy cell leukemia. When combined with DBA44 its diagnostic value for hairy cell leukemia increases significantly
  • Confirmation of giant tumor of bone/soft tissue

Selected references

  1. https://en.wikipedia.org/wiki/Tartrate-resistant_acid_phosphatase
  2. Ljusberg J, Wang Y, Lång P, et al . “Proteolytic excision of a repressive loop domain in tartrate-resistant acid phosphatase by cathepsin K in osteoclasts”. J. Biol. Chem. (2005) 280 (31): 28370–81. doi:10.1074/jbc.M502469200. PMID 15929988.
  3. Went P Th1, Zimpfer A, Pehrs A-C,  et al. High specificity of combined TRAP and DBA.44 expression for hairy cell leukemia. Am J Surg Pathol.2005 Apr;29(4):474-8. doi: 10.1097/01.pas.0000155152.56736.06. PMID: 15767800