Long-acting immune responses including plasma cells and alteration of sebaceous glands cause atrophic scar formation in acne patients

Background: Possible outcomes of acne lesions are atrophic scars which may cause serious physical and psychological distress. Current treatments of post-acne scarring remain difficult and often require invasive procedures. Pathophysiological studies on acne scaring investigated only the first week of papule life. Objectives: Study the pathophysiology of atrophic acne scar formation to identify molecular and cellular pathways that can lead to new therapies for the prevention of acne scarring. Methods: Large-scale gene expression profiling of uninvolved acne skin and acne papules of 48 hours and 3 weeks of age, respectively, of both, scar-prone (SP) and non-scar-prone (NSP) patients was performed. Immunohistochemistry techniques were applied to confirm transcriptomics results on the protein and cellular level. Results: Gene expression and immunohistochemistry analyses showed a very similar immune response in 48 hours-old papules in SP and NSP populations characterized by elevated numbers of T cells, neutrophils and macrophages. However, only in SP patients the immune response persisted in 3 week-old papules, and was characterized by an important infiltrate of B cells. Transient down-modulation of genes related to lipid metabolism was observed in 48 hours-old papules in NSP patients, followed by normalization of gene expression levels after 3 weeks. In contrast, in SP patients a drastic reduction of lipid metabolizing enzymes was observed in 3 week-old papules, suggesting irreversible modifications. The affected lipid metabolism genes were found preferentially expressed in human sebaceous glands, pointing to a destruction of sebaceous gland structures after 3 weeks of inflammatory remodelling in SP acne patients. Total of 54 chips. 18 Non-scar-prone and Scar-prone patients : 3 biospies per patient: 1 in non-lesional skin (Back), 1 on papule less than 48 H old (Back), 1 on skin with papule of 21 days old (Back).