Immunohistochemical Expression of Plasmacytoid Dendritic Cell Markers in Cutaneous Lupus Erythematosus Subtypes in Skin of Color.

Abstract: The role of plasmacytoid dendritic cells (PDCs) has been studied in the cutaneous lupus erythematosus (CLE) to differentiate from their mimickers. We aimed to study the expression pattern of PDC markers in CLE subtypes, analyze their association with histopathological findings, and correlate them with disease activity in skin of color. This cross-sectional study included 115 newly diagnosed CLE cases [acute CLE = 41; discoid lupus erythematosus (DLE) = 72, subacute CLE = 2] from January 2022 to July 2024. Immunohistochemistry (IHC) for CD123, blood-derived dendritic cell antigen-2 (BDCA2), and human myxovirus resistance protein A (MXA) were performed in all cases. In DLE, the mean percentage of CD123 + cells in the superficial dermis (28.36 ± 2.584 vs. 23.05 ± 3.123) and deep dermis (14.83 ± 2.567 vs. 12.24 ± 3.377) were higher than in ACLE. No significant difference was noted in BDCA2 and MXA scores between DLE and ACLE. ACLE was marked by the absence of clustering (P = 0.01, 73.2% vs. 44.4%), whereas DLE showed a significant presence of small clusters (P = 0.01, 33.3% vs. 17.1%) and CD123 + cells at the dermoepidermal junction (P = 0.05, 61.1% vs. 41.5%). A significant association was noted between CD123 + cells at specific locations and histopathological parameters. A linear trend was observed between positivity for CD123, BDCA2, and MXA with ordinal histopathological parameters. These markers did not show any significant correlations with disease activity scores. This is the largest comparative study to highlight the variability in the number, location, and clustering of PDCs among CLE subtypes, possibly relating to their clinical morphology and pathological features.