Memory B-cells are enriched in the blood of patients with acute Buruli ulcer disease: a prospective observational study.

BACKGROUND: Buruli ulcer disease (BUD) caused by Mycobacterium (M.) ulcerans is characterized by necrotic skin lesions. As for other mycobacterial infections, e.g., tuberculosis, the immune response is important for host protection. B-cells may play a role in antimycobacterial immunity but studies characterizing the B-cell repertoire and memory generation in BUD and during the course of treatment are scarce.

METHODS: We investigated the adaptive immune cell repertoire in children with BUD and healthy matched controls by flow cytometry. Analyses prior to treatment, also in a study group of patients with tuberculosis, as well as three time points during BUD treatment (i.e., week 8, 16, and 32) were performed. In addition, BUD disease severity as well as treatment response were analysed for association with B-cell repertoire differences.

RESULTS: Children with BUD had comparable total B- and T-cell proportions but differed largely in B-cell subsets. Memory B-cell (B mem ) proportions were higher in children with BUD whereas regulatory B-cell (B reg ) proportions were lower as compared to healthy controls and tuberculosis patients. Lower naïve (B naïve ) and higher transitional B-cell (B trans ) proportions characterized children with BUD in comparison with tuberculosis patients. Under treatment, B mem proportions decreased significantly whereas proportions of B reg and B naive increased concomitantly in children with BUD. Also, we found significant correlation between lesion size and B mem as well as B reg . However, we did not detect associations between treatment efficacy and B-cell proportions.

CONCLUSIONS: These results suggest a role of B-cell subsets in the immune response against M. ulcerans. Furthermore, changes in B-cell subset proportions may be used as markers for treatment monitoring in BUD.