Recognition of λ1 and λ2 murine light chains by carrierspecific isologous T helper cells; effect of L-H chain assembly

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Abstract
Previous studies from this laboratory have revealed an antigenic site located on the variable domain of the λ2 light chain of BALB/c myeloma protein 315 (the Vλ2315 site). This site is recognized by conventional carrier-specific T helper cells (Th) of BALB/c mice and is expressed on both the free and assembled Vλ2315 domain. The present work defines two new antigenic sites associated with murine λ chains. The first site was associated with free λ1-chain of myeloma protein J558. It was recognized by splenic Th from animals that had been primed with free λ1J558 in complete Freund's adjuvant; when transferred to irradiated animals the primed Th responded to a boost with (4-hydroxy-5-iodo-3-nitro-phenyl)acetate (NIP)-free λ1J558 in saline, but did not respond to NIP-complete J558 or NIP-free λ2315. Priming with complete J558 failed to elicit Th that responded to NIP-free λ1J558. This determinant was therefore only expressed on the free (as opposed to the assembled) form of λ1J558, and it was not shared with free λ2315. The second antigenic site was shared between free λ1J558 and free λ2315. It was defined by free λ2315-primed Th which responded to a boost with NIP-free λ1J558. Since priming with free λ1J558 did not elicit Th that recognized NIP-free λ2315, the cross-reaction was undirectional. The free λ2315-primed Th failed to respond to the complete J558, and M315-primed Th failed to respond to NIP-free λ1J558, indicating that the second (cross-reactive) antigenic site, like the first, was only expressed on free λ chains. Completely reduced and alkylated (unfolded) free λ1J558 and free λ2315 chains elicited Th that recognized native (folded) free chains. Thus, free λ1J558 bears two antigenic determinants recognized by Th, one private and a second shared with free λ2315. λ2315 also bears two determinants, a cross-reactive one on free λ2315 shared with free λ1J558, and a private one located on the Vλ2315 domain of the complete M315. The discussion is focused on possible explanations for the quenching of the two new λ chain determinants upon light-heavy chain assembly and why, by contrast, the private Vλ2315 site is maintained in the complete M315.
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