CD11c+ Memory B Cell Differentiation Across Blood and Tonsil Follows Origin-Specific Routes Revealed by CD24/CD27 Profiling

Atypical B cells (ABCs), characterized by CD11c expression, expand during infection, but their developmental routes and functions remain unclear. Using flow cytometry, single-cell transcriptomics, V(D)J sequencing, and functional assays in human malaria, we mapped ABC differentiation. Two intermediate states emerged: CD27+ switched memory-derived and CD24+ non-switched memory-derived populations. Both converged toward a late ABC phenotype defined by loss of CD21, and reduced plasma cell potential. Pseudotime and clonal analyses showed distinct, isotype-dependent trajectories accompanied by progressive CD24/CD27 loss. In vitro stimulation recapitulated this progressive loss of CD24 and CD27. Similar subsets were also present in healthy blood and tonsils, where class switching and CD86 expression were more frequent, consistent with recent T cell interaction. Thus, combined CD11c, CD24, and CD27 profiling resolves ABC heterogeneity and reveals origin-dependent pathways across tissues, providing a framework for future studies in health and disease, and addressing limitations of previous nomenclature approaches.