LOCATION AND SEQUENCE OF REARRANGED IMMUNOGLOBULIN GENES IN HUMAN THYMUS

Thymic B cells are a proliferating B cell population concentrated in n ormal thymic medulla. They are large cells, some with dendritic morpho logy, and are not associated with any organized follicular structure. Previous work in this laboratory has shown that most of these B cells are surrounded by tightly adherent thymocytes. The literature on human thymic B cells contains many inconsistencies. There is no consensus o n whether they express CD5. Even the existence of thymic B cells has b een questioned. In this study we have undertaken the first analysis of rearranged immunoglobulin (Ig) genes, looking in particular for evide nce of affinity maturation. The Ig V-H genes of human thymic B cells i n this study are those of the fetal repertoire, though the resemblence to fetal Ig genes is limited in other respects. They are mostly unmut ated, but the presence of mutated sequences suggests that this is not a uniform population, as has been previously indicated by phenotypic s tudies.