Immunoglobulin-containing cells in chick embryo urogenital tissues: a new site for early B lineage cells in endothermic vertebrates.

We have employed histological and immunofluorescent staining procedures in order to characterize the distribution of mu + B lineage cells in tissue sections prepared from developing chicken embryo urogenital tissues (UGTs) between 14 and 21 days of incubation. B lineage cells were observed in tissue sections prepared from developing UGTs, especially the mesonephros and its associated tissue, throughout the sample period. The highest densities of mu + B lineage cells were observed in tissue sections prepared from 18 day embryos. The mu + UGT cells were distributed singly and in clusters in subcapsular regions and within the peritubular interstitium of the mesonephros. These observations (1) are consistent with those which suggest nonbursal site(s) for origin of cells in B lineage, (2) may help account for the varying effects of embryonic caudectomy performed between the second and third days of incubation and surgical bursectomy performed close to hatching, (3) may help provide new insights on the effects of sex hormones on B cell development, and (4) suggest fundamental ontogenetic and phylogenetic similarities between developing vertebrate immune systems.