Monoclonal plasma cell infiltrates in the setting of cutaneous follicular helper T cell lymphoproliferative disorders.

There is a growing recognition that some primary cutaneous T cell lymphomas of the skin exhibit a follicular helper T cell phenotype best exemplified by primary cutaneous CD4+ small/medium sized pleomorphic T cell lymphoma. The follicular helper T cells is an evolutionary function in a common TH1 cell under the influence of other cell types most notably monocyte derived dendritic cells but also plasma cells. In addition, the skin defines a characteristic organ site of involvement for angioimmunoblastic T-cell lymphoma (AITL); the first recognized form of follicular helper T cell lymphoma. One of the hallmarks of the follicular helper T cell lymphomas a significant degree of post germinal center B cell hyperplasia. We encountered 7 cases of primary cutaneous follicular helper T cell and four cases of AITL, in which the biopsies contained a light chain restricted plasma cell infiltrate in the skin. There were no features that suggested an atypical or more aggressive clinical course in association with the identification of this light chain restricted plasmacytic infiltrates except one case of AITL in whom a diffuse large cell B cell lymphoma subsequently developed. There was no association with Epstein-Barr virus (EBV) infection light chain restricted plasma cell infiltrate in any of the eleven cases. The basis of these infiltrates is likely a reciprocal functional one reflecting the role of follicular helper T cells in the induction of B cell hyperplasia and the role of plasma cells as a countercheck balance controlling the extent of follicular helper T cell hyperplasia. B cell clonality, plasma cell atypia and blastic B cell transformation can occur without implying a malignant transformation.