CD1

There are four isoforms of the CD1 proteins, designated CD1a, 1b, 1c and 1d.

Anti-CD1a clone 010 is effective in paraffin-embedded tissue: other antibodies require fresh frozen tissue2.

Immunohistochemical expression

CD1a, 1b and 1c are expressed by a range of antigen-presenting cells. CD1d is expressed by gastrointestinal epithelium and B lymphocytes.

• Langerhans' cell and interdigitating reticulum cells

• CD1a: juvenile xanthogranuloma

• 70% of thymocytes, but not early thymocytes or mature T lymphocytes

• some T-ALL/T-LBL

• all post-thymic T-CLL, T-PLL, Sezary's syndrome, cutaneous T cell lymphoma and nodal T-cell lymphoma are CD1 negative

• There is depletion of CD1a-positive dendritic cells in cutaneous B-cell lymphoma but not pseudolymphoma:

Diagnostic utility

• CD1a with S-100: Langerhans' cell histiocytosis

• Classification of thymomas: cortical thymomas are CD1+.

• CD1a positivity may be useful in distinguishing thymic carcinomas from pulmonary neoplasms1.

• Possible in the diagnosis of cutaneous B-cell lymphomas, which are depleted of CD1a+ dendritic cells3.

• CD1a expression by peripheral T-cells is abnormal and is evidence of neoplasia.

References

1 S Pomplun. Immunohistochemical markers in the differentiation of thymic and pulmonary neoplasms. Abstract 158, Pathological Society of Great Britain and Ireland January 2001.

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

3 Schmuth M, Sidoroff A, Danner B, et al. Reduced number of CD1a+ cells in cutaneous B-cell lymphoma. Am J Clin Pathol 2001; 116:72-8

©SMUHT/PW Bishop