Cellular, intracellular, and developmental expression patterns of murine SWAP-70

SWAP-70 is part of a protein complex that catalyzes cell-free DNA recombination between immunoglobulin heavy chain gene switch region substrates. This report studies the expression pattern of SWAP-70 in mouse tissues, sorted cells, and cultured primary cells. SWAP-70 RNA is strongly increased upon switch-induction of spleen cells, and very weakly expressed in thymus and bone marrow. SWAP-70 protein is specifically expressed in B cells, and levels increase rapidly after stimulation. Tissue staining shows strong expression in germinal center B cells, while macrophages and T lymphocytes do not stain. SWAP-70 is not detected in early B cells in the bone marrow. Its expression during mouse ontogeny after birth correlates with the appearance of non-IgM isotypes. While SWAP-70 localizes to the cell nucleus in activated B cells, it is not tightly associated with the chromatin and is found in the cytoplasm as well. SWAP-70 expression is not increased by γ or UV irradiation of spleen cells, nor does it depend on p53. These characteristics are consistent with the putative role of SWAP-70 in immunoglobulin class switching.