T Helper Lymphocytes Recognize the VL Domain of the Isologous Mouse Myeloma Protein 315

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Abstract
Localization of a major determinant on an isologous myeloma protein (M315) which stimulates BALB/c helper T [thymus-derived] cells was investigated. Augmentation of the adoptive secondary antibody response to NIP[4-hydroxy-3-iodo-5-nitrophenylacetyl azide]-M315 and the idiotype of M315 (Id315) was used as an indicator of helper effects. Spleen cells primed with the L chain of M315 (L315) and its V[variable region]-domain (VL315) were highly efficient helpers; priming with the fragment containing the 2 V-domains of M315 (FV315) induced a somewhat weaker helper effect than L315 or VL315. The helper effect was abolished or markedly reduced by treating primed cells with rabbit anti-brain .theta. + C [complement]. Cells primed with the H chain of M315 (H315) effected weak but significant help. The V-domain of H315 (VH315) was incapable of eliciting cells with detectable helper effect.The VL315 apparently embodies a major determinant for T helper lymphocytes. This determinant is expressed on the free VL315 and on the complete M315. Previous studies showed that BALB/c antibodies produced against Id315 recognize antigenic sites that are only displayed on associated (VL315 +VH315) domains.