B220^- bone marrow progenitor cells from New Zealand Black autoimmune mice exhibit an age-associated decline in pre-B and B-cell generation

New Zealand Black (NZB) autoimmune mice exhibit progressive, age- dependent reduction in bone marrow pre-B cells. To ascertain the capacity of NZB bone marrow B220^- cells to generate pre-B cells in a supportive environment, B-lineage (B220⁺) cell-depleted and T-cell-depleted bone marrow cells from NZB mice at 1 to 3, 6, and 10 to 11 months of age were adoptively transferred into irradiated (200R) C.B17 severe combined immunodeficient (SCID) mice. Bone marrow pre-B cells (sIgM CD43[S7] B220⁺) were assessed 3 and 10 weeks posttransfer. Pre-B cells and B cells were reconstituted in SCID recipients of older NZB progenitor cells by 10 weeks posttransplant, in contrast to the very low numbers of pre-B cells present in the donor bone marrow. However, B220 bone marrow progenitor cells from greater than 10- month-old NZB donors were deficient in the reconstitution of both pre-B and B cells in SCID recipients at 3 weeks posttransfer. This reflected a slower kinetics of repopulation, because older NZB → SCID recipients had numbers of both pre-B and B cells similar to recipients of young NZB progenitor cells by 10 weeks posttransplant. Adoptive transfer of equal mixtures of BALB/c and older NZB bone marrow B220^- progenitor cells into irradiated C.B17 SCID recipients failed to demonstrate active suppression. These results suggest that, with age, NZB bone marrow has reduced numbers and/or function of early B220^- B-lineage progenitors. Consistent with this hypothesis, B220^- bone marrow cells from older NZB mice were deficient in progenitors capable of yielding interleukin-7 (IL-7) responsive pre-B cells in vitro on stimulation with the pre-B-cell potentiating factor, insulin-like growth factor 1 (IGF- 1).