CD68 (KP1, PG-M1)

This is the macrophage marker in most widespread routine use. The antigen is expressed by a cytoplasmic protein associated with lysosomes.

Antibodies are effective on paraffin-embedded tissue2.

Immunohistochemical expression

• monocytes

• macrophages

• neutrophils (KP1, not PG-M1)

• basophils

• large lymphocytes

• myeloid precursors (KP1 not PG-M1)

• osteoclasts

• mast cell (PG-M1, not KP1)

• synovial cells (PG-M1, not KP1)

• Langerhans' cell histiocytosis

• interdigitating reticulum cell sarcomas

• melanomas1

Diagnostic utility

CD68 is less specific than is CD163 as a marker of monocyte/macrophages.

• true histiocytic lymphomas

• AML

  • KP1 recognises M1-M5 types

  • PG-M1 recognises M4 (myelomonocytic)and M5 (monocytic) only

• granulocytic sarcoma (but note some B cell lymphomas show weak cytoplasmic staining).

• "plasmacytoid monocytes" in Kikucki's disease

• mastocytosis

References

1Pernick, N. L., DaSilva, M., Gangi, M. D., Crissman, J., Adsay, V. "Histiocytic markers" in melanoma. Mod Pathol 1999;12:1072-7.

2Leong A S-Y, Cooper K and Leong FJ W-M. Manual of diagnostic antibodies for immunohistology. 2nd edition, 2003

©SMUHT/PW Bishop