Early expression of human J chain and mu chain gene in the fetal liver

The expression of J chain and mu chain genes has been investigated during human fetal ontogeny by the polymerase chain reaction performed on liver sections. With this technique, we have been able to detect expression of J chain and mu chain in a single 6-10-microns-thick formalin-fixed paraffin-embedded section of fetal liver tissue. J chain expression reached a maximum at 16 weeks of gestation but was clearly detectable in the liver at the 6th week. Although not detectable at the 6th week, mu chain mRNA became readily detectable at 7 weeks of gestation. These results indicate that J chain expression precedes that of mu chain by at least one week. Therefore, our results imply that J chain is the first immunoglobulin-related polypeptide expressed during the embryogenesis and differentiation of B cells in the fetal liver.