Identification of Liver Epithelial Cell-derived Ig Expression in mu chain-deficient mice

摘要: Growing evidence indicates that B cells are not the only source of immunoglobulin (Ig). To investigate this discovery further, we used mu MT mice, which have a disruption of the first transmembrane exon of the mu heavy chain and do not express the membrane form of IgM. These mice lack mature B cells and thus serve as a good model to explore Ig expression by liver epithelial cells. We found that Ig heavy chains (mu, delta, gamma and alpha) and light chains (kappa and lambda) were expressed in sorted liver epithelial cells of mu MT mice. Surprisingly, each heavy chain class showed its respective variable region sequence characteristics in their variable region, instead of sharing the same VDJ usage, which suggests that class switching does not occur in liver epithelial cells. Moreover, the gamma and alpha chains, but not the mu and delta chains, showed mutations in the variable region, thus indicating that different classes of Ig have different activities. Our findings support the concept that non-B cells, liver epithelial cells here, can produce different classes of Ig.