Figure 4. Bi-compartmental B cell lineage contributing to OCB production in patient MS-2.

Shown are the lineage tree (hierarchic layout; A) and alignment (B) of IgG-VH aminoacid sequences from CSF and PBMC. Lineage trees are calculated using nucleotide sequences IgTree software and displayed using Cytoscape (see Methods). In the lineage tree, each round node represents at least one unique IgG-VH sequence ranging from at least the 5’ end of H-CDR1 to the 3’ end of H-CDR3; larger nodes represent up to hundreds of identical sequences. CSF derived IgG-VH are represented by blue nodes, PB derived IgG-VH are red, and identical sequences found in both compartments are green. Numbers between nodes are numbers of nucleotide mutations; unlabeled connections between nodes represent single nucleotide mutations. Putative germline sequences were determined using SoDA²⁴ and are labeled black; hypothetical intermediates calculated by IgTree are beige. Numbers on lines between nodes (edges) represent mutational steps (nucleotides) between nodes. Triangular nodes contain 2 or more singleton sequences in leaves. The OCB peptide (YFAWSAGK) identified from IEF band “D” (Figure 1) maps to the H-CDR3 and was only found in a CSF-restricted sub-lineage. Additional sub-lineages in PB and CSF suggest B cell affinity maturation and plasma cell maturation (OCB production) to occur in parallel in both compartments.