A REARRANGED LAMBDA-2 LIGHT GENE CHAIN RETARDS BUT DOES NOT EXCLUDE-CHI AND LAMBDA-1 EXPRESSION

Mice transgenic for the lambda-2 light chain of MOPC 315 were established. In newborn transgenics (TG), lambda-2 was the only light chain found on B cells. However, by day 21, lambda-2high-kappa-low as well as lambda-2low-kappa-high double expresser populations were emerging. lambda-2 was found on an increased fraction of serum immunoglobulins (Ig), this fraction declined with age. Correspondingly, kappa and lambda-1 expression was suppressed in young mice but increased with age. In adult mice kappa or lambda-1 were often co-expressed with lambda-2 in single serum Ig molecules. Most B cell hybridomas from an adult TG secreted lambda-2,kappa mixed molecules and had rearranged their kappa-chain genes. One lambda-2,lambda-1 hybridoma and even a lambda-2,kappa,lambda-1 hybridoma were also found. In conclusion, isotypic exclusion in lambda-2 TG is complete in newborns but becomes increasingly leaky with age. Antigen probably expands the lambda-2low-kappa-high B cell population; this population is most likely the major source of serum Ig in adult lambda-2 TG mice. In contrast, the lambda-2high-kappa-low population, a major fraction of which is CD5+mu-low-delta-low, appears only infrequently to develop into antibody-secreting plasma cells.