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Allelic and Isotypic Light Chain Inclusion in Peripheral B Cells from Anti-DNA Antibody Transgenic C57BL/6 and BALB/c Mice1

Most mature B lymphocytes express one BCR L chain, κ or λ, but recent work has shown that there are exceptions in that some B lymphocytes express both κ and λ and some even bear two different κ L chains. Using the anti-DNA H chain-transgenic mouse, 56R, we find that B cells with pre-existing autoreactivity are especially subject to L chain inclusion. Specifically, we show that isotypic and allelic inclusion enables autoreactive B cells to bypass central tolerance giving rise to B cells that retain dangerous features. One receptor in dual receptor B cells is an editor L chain, i.e., neutralizes or alters self-reactivity of the 56R H chain transgene. We compare the 56R mouse when on the C57/BL/6 background, a strain prone to autoimmunity, with that of 56R when on the BALB/c background, a strain that resists autoimmunity. In the B6.56R mouse, polyreactive B cells with dual L chain move to the follicular B cell compartment. Their localization in the follicular compartment may explain the ease with which B cells in the B6.56R differentiate into autoantibody-producing plasma cells. Likewise, in the BALB/c.56R mouse, dual L chain B cells are found in the follicular B cell compartment. Yet, the lack of autoantibody-producing plasma cells in the BALB/c.56R suggests that postfollicular tolerance checkpoints are intact. The Jκ usage in dual κ L chain B cells suggests increased receptor editing activity and is consistent with the expected distribution of Jκ genes in our computational model for random selection of Jκ.