Type and maturational status of dendritic cells in cutaneous B cell lymphoproliferative disorders

B cell cutaneous lymphoid hyperplasia (B-CLH) and cutaneous mucosa-associated lymphoid tissue (MALT) lymphoma represent opposite poles of the same disease spectrum. We explored the hypothesis that dendritic cells (DCs) are central in the generation and regulation of such lesions.

Immunohistochemistry was used to identify Langerhan cells (LCs), dermal DCs (DDCs) and plasmacytoid DCs (PDCs), as well as mature and alternatively activated DCs, in B-CLH (n = 14) and cutaneous MALT lymphoma (n = 18). PDCs were most numerous in both types of lesion, but there were significantly more PDCs and DDCs and greater numbers of mature DCs in B-CLH. Nevertheless, DCs were still present in cutaneous MALT lymphoma and there were also proportionately more alternatively activated cells.

Mature DDCs are prime activators of naive T cells and our results suggest that they are likely to be largely responsible for driving the initial proliferation in B-CLH. The results also suggest that PDCs play a central role, and we hypothesize that they dictate the magnitude, duration and direction of the response. In cutaneous MALT lymphoma PDCs are the dominant DC subtype, and may act by damping down the antitumour host immune response, as well as directly stimulating the growth and differentiation of the neoplastic lymphocytes.