Abstract
CD5 is expressed by most T cells and a subset of B cells. Human CD5 positive B cells are present in fetal lymphoid tissue, their frequency decreasing with fetal age. In adult human tissues, CD5 positive B cells have been reported to be present in the germinal centre and mantle zone. Malignancies of CD5 positive B cells include mantle cell lymphoma and chronic lymphocytic leukemia. This report describes an immunohistochemical staining technique used to visualise the expression of CD5 by B cells in human fetal intestine, tonsil, and mantle cell lymphoma. B cells in fetal intestine, tonsillar epithelium, and mantle cell lymphoma all had a similar high intensity of CD5 expression. In contrast, CD5 B cells in the mantle and germinal centre expressed very small amounts of CD5, below the threshold of the technique. Therefore, mantle cells and mantle cell lymphoma are not equivalent in terms of CD5 expression.
Key Words: mantle cell lymphoma • CD5 • mantle zone B cells
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Figure 1 Frozen sections of (A) fetal intestine, (B) tonsil, and (C) mantle cell lymphoma, stained using anti-CD3 (immunoperoxidase; brown) followed by anti-CD5 (immunoalkaline phosphatase; blue). Blue CD5 positive B cells are indicated with arrowheads. They are present in the primary follicle in the fetus and the epithelium in the tonsil. Tumour cells in mantle cell lymphoma express CD5 with an intensity comparable to that seen in the fetal primary follicle and tonsillar epithelium. Note that the tonsillar mantle zone is unambiguously CD5 negative.
Figure 2 Frozen sections of tonsil stained with (A) anti-CD3 (immunoperoxidase; brown), followed by anti-CD5 (immunoalkaline phosphatase; blue); (B) anti-CD3 plus anticytokeratin (immunoperoxidase; brown), followed by anti-CD5 (immunoalkaline phosphatase; blue); and (C) anti-CD3 plus anti-CD20 (immunoperoxidase; brown), followed by anti-CD5 (immunoalkaline phosphatase; blue). These serial sections confirm that the blue cells identified with arrowheads in (A) are located in the epithelium because blue cells can be seen within the epithelial network in (B). They also confirm that the blue cells in (A) are B cells because in (C) the blue staining is blocked by CD20.