The impact of lesional inflammatory cellular infiltrate on the phenotype of bullous pemphigoid.

BACKGROUND The influence of cutaneous cellular infiltration on the phenotype of bullous pemphigoid (BP) remains to be established. OBJECTIVES To evaluate the main histopathological characteristics of patients with BP and to assess the association between the composition of lesional inflammatory infiltrate and the various clinical, immunological, and immunopathological aspects of the disease. METHODS Retrospective study encompassing patients diagnosed with BP throughout the years 2009-2020 in a specialized tertiary referral center. RESULTS The study encompassed 136 patients with BP, of whom 27 (19.9%) demonstrated a cell-poor inflammatory infiltrate in lesional skin specimens. Overall, 78 (57.4%), 71 (52.2%), and 5 (3.7%) specimens were found to include eosinophil-predominant, lymphocyte-predominant, and neutrophil-predominant inflammatory infiltrates, respectively. Relative to the remaining patients with BP, those with an eosinophil-predominant inflammatory infiltrate had higher (90.8% vs. 77.2%; P=0.030) while those with a cell-poor inflammatory infiltrate lower (70.3% vs. 88.7%; P=0.017) seropositivity of anti-BP180 NC16A IgG. The latter subgroup presented with higher prevalence of mucosal involvement (25.9% vs. 8.3%; P=0.011) and a non-inflammatory clinical phenotype (50.0% vs. 17.1%; P=0.041). Patients with lymphocyte-predominant inflammatory infiltrate manifested with higher severity BPDAI scores and a lower frequency of the non-inflammatory subtype (11.1% vs. 36.4%; P=0.035), whilst those with a neutrophilic infiltrate presented with lower mean (SD) levels of anti-BP180 NC16A IgG (269.3[227.6] vs. 722.7[1,499.6] U/ml; P=0.003). CONCLUSIONS Eosinophil-predominance and high cellularity in lesional inflammatory infiltrate of BP skin are associated with increased seropositivity of anti-BP180 NC16A IgG. Lymphocyte-predominant infiltrates predict a more severe phenotype, pointing towards a pathogenic role of autoreactive lymphocytes.