WHITHER THE ANERGIC B-CELL

The kinetics of potentially autoreactive B-cells were investigated in a double-transgenic model of self-tolerance. Two types of transgenic m ice were created for this purpose. In the first the great majority of B-cells expressed the rearranged heavy and light chain genes encoding a high affinity receptor for hen egg lysozyme (HEL), while the second type expressed HEL in either soluble (sHEL) or membrane-bound (mHEL) f orm. Double-transgenic (Dbl-Tg) mice were produced either by mating th e two types of founders or by transferring bone marrow cells from Ig-t ransgenic (Ig-Tg) donors into irradiated HEL-Tg recipients. The lifesp an of B-cells from the Dbl-Tg mice was measured by oral loading with t he thymidine analogue, 5-bromo-2'-deoxyuridine (BrdU) for periods vary ing from three days to six weeks. Experiments in various combinations of Dbl-Tg mice revealed a three-tiered hierarchy of B-cell unresponsiv eness, each level of which was characterised by a different B-cell lif espan. Exposure to mHEL led to rapid deletion of B-cells at an immatur e stage in their development with a median lifespan of approximately 1 5 hours. B-cells exposed to sHEL above a critical tolerogenic threshol d were not deleted in the bone marrow but migrated to the spleen in an anergic stale where they died within three days. If the receptor occu pancy of sHEL was below the tolerogenic threshold, B-cells were neithe r deleted nor rendered anergic tie were ''indifferent'') and had a nor mal median lifespan of four to five weeks. A number of conclusions wer e derived from these studies: (i) there is a correlation between recep tor occupancy by self antigen and B-cell lifespan; (ii) anergy and del etion in self-reactive B-cells appear to be part of a spectrum of unre sponsiveness rather than being totally discrete molecular entities;(ii i) a lack of T-cell help in addition to receptor occupancy is a crucia l factor in determining the relatively short lifespan of anergic B-cel ls; and (iv) B-cells from young mice have a higher turnover rate than in adult mice suggesting selection of newly-generated B-cells into the long-lived repertoire; the short lifespan of tolerant self-reactive c ells further implies a major role for negative selection in this proce ss.