Most marginal zone B cells in rat express germline encoded Ig VH genes and are ligand selected

The present study was performed to analyze whether marginal zone B (MZ-B) cells in nondeliberately immunized adult rats are selected on basis of the specificity of their B cell receptor, and to determine to what extent memory B cells contribute to the MZ-B cell subset. To this end, the Ig PC7183 V(H) gene repertoire was studied among V(H)DJ(H)-mu transcripts expressed in four sequential stages of B cell development, of two individual untreated adult rats. B cell subsets, i.e., pro/pre-B cells and newly formed B (NF-B) cells from bone marrow, and recirculating follicular B cells and MZ-B cells from spleen were sorted by flow cytometry. In addition, from one these rats, cells were microdissected from follicular and MZ areas of the spleen and productive PC7183 V(H) gene rearrangements were analyzed for the presence of somatic mutations. Sequence analysis reveals that most MZ-B cells in the adult rat, either defined by flow cytometry or by their anatomical location in the spleen, express germline encoded V(H) genes (naive MZ-B cells) and a minor fraction (about 20%) of the MZ-B cells carry somatic mutations (memory MZ-B cells). In addition, we show that naive MZ-B cells are a selected population of cells, both based on PC7183 V(H) gene repertoire and on the length of the Ig heavy (H) chain complementarity-determining region 3 (H-CDR3) region, i.e., PC7183 V(H)DJ(H)-mu transcripts of MZ-B cells carry significantly shorter H-CDR3 regions than other B cell subsets.