Cutting edge: Senescent BALB/c mice exhibit decreased expression of λ5 surrogate light chains and reduced development within the pre-B cell compartment

Although senescent BALB/c mice (~2 years old) have reduced numbers of small pre-B cells, early pre-B cells (CD43⁺CD25⁺B220⁺) are present in comparable numbers within the bone marrow of both young (3-6-month-old) and senescent BALB/c mice. The transition of CD43⁺ pre-B cells to the CD43- pre- B cell compartments is dependent on proliferation and clonal maturation dictated by the pre-B cell receptor (μ/λ5/VpreB). In vivo, senescent CD43⁺B220⁺ pro-B/early pre-B cells demonstrated reduction of λ5 mRNA, by RT-PCR analysis, and of both surface and cytoplasmic λ5 protein. Decreased λ5 protein expression was also seen among pro-B/pre-B cells derived from senescent bone marrow after stimulation in vitro with IL-7. We propose that diminished expression of the λ5 surrogate light chain results in decreased pre-B cell receptor formation and contributes to reduced recruitment of nascent CD43⁺ pre-B cells into the CD43^- large and small pre-B cell compartments.