Synthesis of λ light chain subtypes by stimulated and unstimulated mouse B cells

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Abstract
Inbred mouse make 3 λ chain subtypes. The λ1 and λ3 chains have similar variable (V) regions (in both the same V gene segment [Vλ1] is used), whereas λ2 and λ3 have similar constant (C) regions. Despite the λ1 and λ3 V region similarity, λ1 occurs much more frequently than λ3 (and λ2) in the serum immunoglobulins and antibody responses of most inbred strains of mice. To explore the basis for the λ1 predominance, we compared the rates of synthesis of the 3 subtypes and the frequencies of the B cells that synthesize them, focussing on “resting” (i.e., unstimulated) and on polyclonally stimulated B cells from spleens of unimmunized BALB/c mice. In resting cells the relative rates of synthesis and the relative frequencies of the respective B cells were in accord, indicating that the rate of λ chain synthesis is approximately the same per resting B cell, regardless of the λ subtype it produces. However, in the polyclonally stimulated cells, λ1 was made 7 times faster than λ2 and 10 times faster than λ3; normalizing these rates by the frequencies of the respective stimulated cells suggests that in stimulated B cells λ1 chains are made 5 times faster per cell than λ2 or λ3, while the latter are made at about the same rate per cell. In view of the marked structural homology between λ2 and λ3 genes in segments other than the V‐gene segment, we suggest that the pronounced differences among polyclonally stimulated B cells in expression of the genes for the various λ subtypes may be due to the presence of less potent enhancer‐like sequences in the λ2 and λ3 genes than in the λ1 gene.