Consequences of receptor editing at the λ locus: Multireactivity and light chain secretion

Abstract

To investigate the manner in which B cells with light (L) chains undergo receptor editing, we have studied hybridoma panels from 56R͞-deleted (kdel) mice. 56R͞kdel mice only produce four L chains (1, 2, 3, and X). They also have a simplified heavy (H) chain repertoire: All B cells start out with a 56R anti-DNA H chain. A few frankly autoreactive 56R 1 cells appear to escape into the periphery, but the majority of the peripheral B cell repertoire in 56R͞kdel is made up of B cells expressing the 56R H chain with the X L chain. Surprisingly, 56R X B cells are multireactive, binding to a variety of self and nonself antigens, including dsDNA (albeit at reduced affinity compared with the other L chains). Another significant population in the 56R͞kdel mouse consists of allelically included B cells that express X along with another L chain. The multireactivity of both 56R X and 56R X͞1 receptors could contribute to autoimmunity if these B cells were to become activated. Also found among 56R͞kdel hybridomas are clones that have inactivated the H chain and secrete only L chains. These clones may represent products of exhaustive rearrangement. Multireactivity, allelic inclusion, and L chain secretion are three consequences of editing at the locus that may predispose toward the development of autoimmunity.olerance to self-antigens can be achieved by replacing autoreactive heavy (H) chain and light (L) chain V genes with V genes coding for nonself receptors, a mechanism called receptor editing (1-4). Several recent studies support a pivotal role for receptor editing in the generation of a tolerant B cell repertoire (5-7). The L chain locus uses the nested organization of V and J gene segments for secondary rearrangements that can replace or inactivate a VJ that contributes to autoreactivity ( Fig. 3 Top, which is published as supporting information on the PNAS web site). editing can also delete and͞or inactivate an autoreactive chain by rearrangement to the de (human) or to RS (mouse) (8-10). Secondary rearrangements to J and deleting elements are presumed to be unidirectional; hence, editing enriches the repertoire in J5 rearrangements. Editing also increases the frequency of B cells that are rearranged at both alleles (3,(11)(12)(13). Rearrangement at the second L chain isotype, , can rescue -inactivated and -deleted B cells (1,14).L chain genes also contribute to autoreactivity and require editing. The mouse locus has two separate clusters, each consisting of V and JC gene segments (Fig. 3 Middle) (15, 16). In one cluster, V1 rearranges either to J1 or J3. In the other cluster, V2 or VX rearranges to J2 (15). Rearrangements that leapfrog across clusters (for example, V2 to J1) are very infrequent (15). Thus a B cell with a rearrangement that yields a self-reactive receptor is in a dangerous position because of its inability to delete the primary rearrangement.H chain variable region gene segment (V H ) genes can also be edited because a VDJ gene can be replaced by secondary rearrangement of an upstream V H to a partial RS...

Antigen Receptor Editing in Anti-DNA Transitional B Cells Deficient for Surface IgM

“…9A. Our binding results are consistent with those of Doyle et al (60) who also found 56RV x-expressing B cell hybridomas to produce Ab with specificity for dsDNA, but they differ from those of earlier reports showing the V 21D and V x editors to inhibit completely the binding of 56R to dsDNA (4,18,50). The basis for the difference is unclear.…”

Four primordial immunoglobulin light chain isotypes, including λ and κ, identified in the most primitive living jawed vertebrates

“…It is also curious that both N region diversity and somatic hypermutation often result in arginines encoded in CDR3. This raises the possibility that Igr could be selected to bind a particularly charged antigen moiety; paratopes with arginine have been implicated in anti-DNA-mediated autoimmunity [18]. Eleven arginine residues not encoded by V or J segments are found in just the 22 CDR3 reported here.…”

Editing and escape from editing in anti-DNA B cells

“…B cell hybrids expressing VH56RϩV 38c IgM (hybridoma 160.3) and VH56RϩV 21D IgM (hybridoma 79.1) were derived from a VH56R mouse with graft-versus-host disease (15). In addition, we used VH56R/76RϩV 38c IgM and IgG hybridomas (30) and a VH56RϩV x IgM hybridoma (25). The hybridomas used in this study were analyzed by RT-PCR and ELISA to minimize the possibility of allelic and isotypic inclusion (15,25).…”

“…In addition, we used VH56R/76RϩV 38c IgM and IgG hybridomas (30) and a VH56RϩV x IgM hybridoma (25). The hybridomas used in this study were analyzed by RT-PCR and ELISA to minimize the possibility of allelic and isotypic inclusion (15,25).…”

“…The autoreactive H/L combination escapes central tolerance and gains access to the periphery because, we presume, the nonautoreactive H/L pair dilutes the expression of the autoreactive pair. Since we discovered this type of partially edited B cell, many examples of allelic or isotypic inclusion have been observed (15,(22)(23)(24)(25), including additional transgenic (Tg)-encoded autoreactivities (26,27) and autoreactivities present within an unperturbed repertoire (11,28). Such B cells have been referred to as ''Trojan horses'' and may, if activated in the periphery, pose a risk of autoimmunity.…”