T helper cell recognition of idiotopes on λ2 light chains of M315 and T952: evidence for dependence on somatic mutations in the third hypervariable region

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Abstract
Previous work has indicated that BALB/c T helper cells (Th) recognize an idiotope expressed on a 88-114/117 fragment of Vλ2 of BALB/c myeloma protein 315. In the present study the antigenic structure of this idiotope was further analyzed. Conventional carrier-specific Th elicited by immunization of BALB/c mice with free λ2315 did not cross-react with the free λ2 chain of the BALB/c myeloma protein T952 which differs from λ3″ in five amino acid positions (38,94, 95,96, 99). Similarly, Th primed with free λ2T95 did not respond to a boost with free λ2315. Thus, BALB/c h2315-specific Th recognize an idiotope that depends on some or all of the residues at positions 94, 95, 96 and 99. Furthermore, free λ2T952 contains an idiotope immunogenic to Th that depends on some or all of residues 38, 94, 95, 96 and 99. Th recognition of the free λ2T952 idiotope was quenched upon H + L chain assembly because Th elicited by free λ2T952 did not respond to a boost with the complete T952 myeloma protein. In contrast to the lack of Th cell cross-reactivity, some of the antisera from BALB/c mice immunized with free λ2T952 cross-reacted with free λ315, free λJ558 and free λ3CBPC49 but not with free ϰw3129 or polyclonal L chains. The H chain of T952 (α,ϰ2) myeloma protein was abnormally short (Mr = 48 000) and T952 existed as a halfmere probably due to this H chain deletion. Furthermore, H and L chains were disulfide bonded to each other.