Studying cutaneous mastocytosis, we observed an unusual phenotype expression of lymphoid-associated antigens (Table ). With the exclusion of the reported reactivity of neoplastic mast cells for Bcl-2 [1], CD22 and CD2 [2], to the best of our knowledge, no other lymphoidassociated markers have been shown to be positive in mast cells. CD2 may be regarded as a mastocytosis-specific mast cell marker [3], even if not all neoplastic mast cells appeared to react with the antibody. The Bcl-2 positivity could be justified by the very long survival of mast cells, but the described reactivity [1] is not in agreement with that observed by other authors [3].
We verify the strong reactivity of mast cells to a pan-T antigen, CD45RO, clones UCHL1 and A6 (Fig. ), without any positivity for CD3 and CD5, and the aberrant reactivity for CD10 (CALLA) and Cyclin D1. CD10 is expressed by a wide variety of non-neoplastic hematopoietic, epithelial, and mesenchymal stromal cells and tumors [4], and thus it is not surprising to find reactivity in mast cells. Cyclin D1 (Bcl-1) belongs the family of Bcl proteins, which regulate the cellular survival: this finding is coherent with the proven Bcl-2 and Bcl-x positivity [1].
Hence, it is important to know these immunohistochemical findings in mast cell diseases, to exclude incorrect diagnoses of lymphoproliferative diseases.
ACKNOWLEDGMENT
The authors thank Ms. Celeste Scotti, Ms. Barbara Albumi, and Ms. Luisella Brugnoli for their technical assistance.