Lineage Tree Analysis of Human Memory B Cells

The human adaptive immune system relies on the diversity and specialization of B cells to mount an effective response against pathogens and antigens. Memory B cells represent distinct and functional subsets and isotypes with different origins and immunological roles within the human body. This study aims to investigate the clonal relationships and subset specific dynamics of human memory B cells by reconstructing immunoglobulin lineage trees derived from high throughput sequencing data. Three different B cell subsets, CD27+IgD+ (non-switched memory B cells), CD27+IgD- (switched memory B cells), and plasmablasts, from four healthy donors were used as a basis for the analysis conducted in this study. Raw immunoglobulin repertoire data was processed using MiXCR to generate clonotypes and to reconstruct the subsequent immunoglobulin lineage trees. These trees were then used to perform a comprehensive topographical and statistical analysis using R. The statistical analyses included subset and isotype comparisons, evaluations of the different topographical characteristics across subsets and isotypes, intra and interclonal diversity analyses and principal component analysis comparing samples with and without the plasmablast subset. The results demonstrated significant differences in lineage topology between the B cell subsets, with trees containing plasmablasts showing a greater variance in branch length and average depth, suggesting an increased clonal diversification consistent with an active immune response. Moreover, the interclonal and intraclonal diversity comparisons revealed a notable heterogeneity in the subset distribution and isotype usage, reflecting a varied immune history between the donors. It was also shown that the lineage trees containing the IgA isotype displayed a greater difference in characteristics associated with depth. These findings might contribute to a deeper understanding of the structural and functional dynamics of memory B cell subsets and help to underscore the utility of lineage tracing in immunological research.