Stochastic pairing of heavy-chain and kappa light-chain variable gene families occurs in polyclonally activated B cells

Frequencies of 25 immunoglobulin heavy-chain and kappa light-chain variable (VH + V kappa) gene-family pairings expressed in splenic B-cell populations were determined by hybridization of VH- and V kappa-family-specific DNA probes to mitogen-induced B-cell colonies from C57BL/6 mice or hybridomas derived from BALB/c and NZB mice. Both analyses support the conclusion that VH and V kappa gene families pair without bias; as would be expected for random association, the frequencies of specific VH + V kappa pairs may be estimated by the product of the independent VH and V kappa frequencies. Based upon the frequencies at which 9 VH and 12 V kappa gene families are expressed, we calculated the expected usage for approximately 100 VH + V kappa family pairings in neonatal and adult C57BL/6 mice. Variability in the expression of such VH + V kappa pairings is considerable; pairs representing greater than 10% to less than 0.01% of the splenic B-cell population occur. This variability is most pronounced in the neonate, where 6 VH + V kappa family pairs account for nearly 40% of all mitogen-reactive B cells. As the neonate matures, the distribution of frequencies for VH + V kappa pairings becomes more nearly uniform. This process may underlie the patterned acquisition of humoral immune responsiveness.