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Differentiating lichen planopilaris from chronic cutaneous lupus may be as easy as 1,2,3 (actually CD123)

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By Warren R. Heymann, MD
June 4, 2016

My last dermatopathology case of the week was that of a woman with scarring alopecia, which was clearly well advanced. Hardly any follicles remained, and on one section there was a small follicular unit with a peri-infundibular mononuclear infiltrate and slight vacuolar alteration of the follicular epithelium. I signed the case out as “scarring alopecia, most consistent with lichen planopilaris. Although I favor LPP over that of lupus (LE), the latter cannot be completely ruled out”.

Is there a way to be more specific? It appears that there may well be and the answer is as easy as CD123.

Plasmacytoid dendritic cells express CD123. The following abstract by Saadeh et al (1) summarizes their vital role in inflammation:

Plasmacytoid dendritic cells (pDCs) represent a specialized dendritic cell population that exhibit plasma cell morphology, express CD4, CD123, blood-derived dendritic cell antigen-2 (BDCA-2) and Toll-like receptor (TLR)7 and TLR9 within endosomal compartments. When activated, pDCs are capable of producing large quantities of type I IFNs (mainly IFN-α/β), which provide antiviral resistance and link the innate and adaptive immunity. While generally lacking from normal skin, pDCs infiltrate the skin and appear to be involved in the pathogenesis of several inflammatory, infectious (especially viral) and neoplastic entities. In recent years, pDC role in inflammatory/autoimmune skin conditions has been extensively studied. Unlike type I IFN-mediated protective immunity that pDCs provide at the level of the skin by regulated sensing of microbial or self-nucleic acids upon skin damage, excessive sensing may elicit IFN-driven inflammatory/autoimmune diseases. In this review, focus will be on the role of pDCs in cutaneous inflammatory/autoimmune dermatoses.

Kolivras and Thompson performed a retrospective study comparing CD123 immunoreactivity of 35 cases of LPP with 20 cases of LE. (based on classical H&E histology). They determined that the presence of PDCs in clusters is highly predictive (and statistically significant) in diagnosing LE (2). In another study comparing 17 cases of LE, 19 LPP, and 9 CCCA (central centrifugal cicatricial alopecia), PDCs comprised a greater percentage of the infiltrate and were also arranged in clusters, allowing the CD123 stain to differentiate LE from both LPP and CCCA (3).

CD123 represents the alpha chain of the interleukin-3 receptor (IL-3RA). Overexpression of CD123 has been observed in hematologic malignances including acute myeloid and B-lymphoid leukemias, blastic plasmacytoid dendritic neoplasms, and hairy cell leukemia. Recent studies indicate that abnormalities of the alpha-chain of the interleukin-3 receptor (IL-3RA or CD123) are frequently observed in some leukemic disorders and may contribute to the proliferative advantage of leukemic cells. CD123 is overexpressed in the aforementioned hematologic malignancies. Monoclonal antibodies directed to IL-3RA are currently being developed (either as a solitary treatment or fused to other agents such as diphtheria toxin) for the treatment of these lymphoproliferative malignancies (4).

PDCs are thought to play a role in the pathogenesis of lupus based on their production of type I interferons (3). While the capability of differentiating LE from LPP or CCCA by staining for CD123 is certainly intriguing, the potential for using anti-CD123 monoclonal antibodies therapeutically for lupus is absolutely exhilarating.

1. Saadeh D, et al. Update on the role of plasmacytoid dendritic cells in inflammatory autoimmune skin disease. Exp Dermatol 2016; 25: 425-21.
2. Kolivras A, Thompson C. Clusters of CD123+ plasmacytoid dendritic cells help distinguish lupus alopecia from lichen planopilaris. J Am Acad Dermatol 2016; 74: 1267-9.
3. Fening K, et al. CD123 immunohistochemistry for plasmacytoid dendritic cells is useful in the diagnosis of scarring alopecia. J Cutan Pathol 2016 April 30 [Epub ahead of print]
4. Testa U, et al. CD123 is a membrane biomarker and a therapeutic target in hematologic malignancies. Biomark Res 2014; 2: 4.

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