A rearranged λ2 light gene chain retards but does not excludex and λ1 expression

Abstract

Mice transgenic for the λ₂ light chain of MOPC315 were established. In newborn transgenics (TG), λ₂ was the only light chain found on B cells. However, by day 21, λ₂^highx^low as well as λ₂^lowx^high double expresser populations were emerging. λ₂ was found on an increased fraction of serum immunoglobulins (Ig), this fraction declined with age. Correspondingly, x and λ₁ expression was suppressed in young mice but increased with age. In adult mice x or λ₁ were often co‐expressed with λ₂ in single serum Ig molecules. Most B cell hybridomas from an adult TG secreted λ₂,x mixed molecules and had rearranged their x chain genes. One λ₂,λ₁ hybridoma and even a λ₂,xλ₁ hybridoma were also found. In conclusion, isotypic exclusion in λ₂ TG is complete in newborns but becomes increasingly leaky with age. Antigen probably expands the λ₂^lowx^high B cell population; this population is most likely the major source of serum Ig in adult λ₂ TG mice. In contrast, the λ₂^highx^low population, a major fraction of which is CD5⁺μ^lowδ^low, appears only infrequently to develop into antibody‐secreting plasma cells.