V lambda-light chain genes reconstitute immune responses to defined carbohydrate antigens or haptens by utilizing different VH genes

Kappa-deficient mice are non-responders to dextran B512: is this unresponsiveness due to specialization of the kappa and lambda Ig repertoires?

In the dextran B512 high-responder strain C57BL, the response to dextran is restricted to the preferential expression of the V(H)B512 and the V(kappa)OX1 gene combination. The importance of the heavy chain is suggested by the fact that mice with the Ig C(H) allotype, different from C57BL, are low or non-responders to dextran, but the light chain could also play a role. All anti-dextran B512 mAb described to date (>200) use kappa light chains. No anti-dextran antibody using lambda has ever been observed. To ascertain if the restriction of the use of V(kappa) genes in response to dextran B512 was more stochastic or due to other factors, we have studied the response to dextran B512 in C57BL/6 mice where the C(kappa) domain has been disrupted (C57BL.C(kappa)T). These mice are unable to express kappa light chains and their humoral antibodies bear light chains of the lambda type. We found that C(kappa) knockout mice are unable to respond to dextran given in a thymus-independent or -dependent form. The lack of responsiveness is specifically directed to the dextran epitopes since these mice are fully competent to respond to other antigenic structures present in the same immunogenic molecule. These mice are also apparently normal regarding the expression of V(H) genes. Finally, we tested the response to dextran in C57BL.C(kappa)T mice carrying the lpr mutation that was introduced to favor an increase in the life span and make the response to dextran more easily detectable. The introduction of the lpr mutation was not sufficient to change the pattern of unresponsiveness in the C57BL.C(kappa)T mice. We concluded that there are deficiencies in the light chain repertoire because the V lambda light chain could not reconstitute the response to dextran. We discuss the possible mechanisms for this new type of unresponsiveness to dextran B512.

Mutational Analysis of Avidity and Fine Specificity of Anti-Levan Antibodies

Using the polyfructose, bacterial levan, as a model polysaccharide, we analyzed how V regions affect binding in anti-polysaccharide mAbs. Previously, panels of mAb were constructed from bacterial levan-immunized BALB/c and CBA/Ca mice. The BALB/c mAb were mostly germline VHJ606:Vκ11, and a subset contained presumed somatic mutations in the complementarity-determining regions (CDRs) that correlated with increases in avidity for the β(2→1) inulin linkage of levan. The CBA/Ca mAb were more heterogeneous in V gene usage, but a subset of inulin-nonreactive mAb were VHJ606:Vλ and had VH sequence differences in the CDRs from the VHJ606 regions of the BALB/c mAb. In this report, VHJ606 Abs containing various combinations of specifically mutated H and L chains were produced by engineered transfectants and tested for inulin avidity and levan binding. Two presumed somatic mutations seen in CDRs of the BALB/c hybridomas were shown to directly cause marked increases in avidity for inulin (VH N53H, 9-fold; VL N53I, 20-fold; together, 46-fold) but not for β(2→6) levan. Exchange of either positions 50 or 53 in VH or the H3 loop between the BALB/c and CBA/Ca mAb resulted in either fine specificity shift or total loss of bacterial levan binding. Three-dimensional models of the V regions suggested that residues that affect binding to inulin alone are near the edge of the CDR surface, while residues involved with binding both forms of levan and affecting fine specificity are in the VH:VL junctional area.

The primary antibody repertoire of kappa-deficient mice is characterized by non-stochastic Vlamda1 + V(H) gene family pairings and a higher degree of self-reactivity

We have investigated the primary antibody repertoire of genetically manipulated 129/Sv kappa-deficient (JCkappaD) mice, in order to understand the contributions of the lambda-light chain, in the absence of an otherwise predominant kappa-light chain, to the development of humoral immunity. The expression of Vlambda1 gene (lambda1 and lambda3 subtypes) and the Vlambda1 + V(H) (J558, 36-60, V(H)11 and S107) gene family associations were studied in 7.43 x 10(3) mitogen-activated splenic B-lymphocyte clones of JCkappaD origin. Furthermore, the functional significance of the exclusive expression of the lambda-light chain, in the peripheral B-cell repertoire of JCkappaD mice, was analysed by determining natural autoantibody specificities in the circulating serum immunoglobulin and the frequency of autoreactive B-lymphocyte clones in the peripheral B-lymphocyte repertoire. These experiments revealed that: first, of the three available Vlambda genes at the lambda locus, the Vlambda1 gene is the one that is expressed most frequently (59.9%); second, non-random Vlambda1 + V(H) (J558, 36-60) gene family pairings occur in kappa-deficient mice; and third, a higher degree of self-reactivity is generated as a result of exclusive use of the lambda-light chain, as evidenced by higher levels of serum natural autoantibodies as well as a high frequency of autoreactive B-lymphocyte clones in kappa-deficient (129/Sv JCkappaD) mice. These observations suggest that the high murine kappa/lambda ratio in mice may, apart from high sequence diversity at the kappa-locus, be a result of endogenous selection against the lambda-light chain to restrict self-reactivity within the homeostatic threshold.