Re-evaluation of the probabilities for productive rearrangements on the kappa and lambda loci

V-J rearrangements at Ig light chain (IgL) genes occur in resting small pre-B cells. In the absence of cell division, the probability of productive kappa and lambda rearrangements is proportional to the output of K+ B and lambda(+) B cells in bone marrow. The kinetics and probability of productive kappa or lambda. rearrangements was assessed in three groups of mice carrying two (wild-type), one or no intact Ig kappa gene, and the following conclusion are drawn. kappa and lambda rearrangements occur independently at different kinetics, and rearrangements are initiated at a time when kappa rearrangements are stopping. The probability of productive kappa and lambda rearrangements per chromosome is calculated to be similar to 60 and similar to 20% respectively. Thus, a kappa gene can attempt rearrangements up to three times per chromosome during a cell development, These findings explain that the observed ratio of K+ B/lambda(+) a cell production in wild-type mice is 95/5.