Plasmacytoid monocytes have been identified in patients with granulomatous lymphadenitis, including those with mycobacterial disease, using an antibody to CD123. These cells were found to secrete large amounts of Type 1 interferon (principally interferon alpha) (1). Similar cells have been produced in vitro and after activation by interleukin 3 (IL-3) or CD40L have developed a dendritic cell morphology. Hence they are now called plasmacytoid dendritic cells (pDCs) (2).
Some of the biopsies in this publication contain epithelioid cells. It will be important to determine whether these cells stain positively to an antibody to CD123, in which case epithelioid cells are a mature form of pDCs. . pDCs also express Toll Receptors (TLRs) 7 and 9 and could be identified in these epithelioid cells (details described in Ref 2)
pDCs are one of the cells of the innate immune system . We have developed an model of tuberculoid leprosy using an antigen in human sensory nerve, suggesting that the human disease may be an autoimmune disorder of the innate immune system rather than a delayed hypersensitivity response to Mycobacterial leprae antigens (3).

1.Cella M, Jarrossay D, Facchetti F, et al. Plasmcytoid monocytes migrate to inflamed lymph nodes and produce large amounts of Type 1 interferon. Nat Med 1999; 5: 919-923.
2. Marafioti T, Paterson JC, Ballabio E, et al. Novel markers of normal and neoplastic human plasmacytoid dendritic cells Blood 2008; 11: 3779-3792.
3. Crawford CL, Hardwicke PMD. Experimental leprosy: a model of epithelioid cell granuloma. Int J Dermatol 2011; 50: 255-261.