Idiotype-specific Ly-1 B cell-mediated helper activity: hybridomas that produce anti-idiotype antibody and nonimmunoglobulin lymphokine(s)1.

Previous work has shown that the expression of a predominant family of idiotypic determinants (NPb) in the in vitro response to the 4-hydroxy-3-nitrophenyl acetyl (NP) hapten is dependent on helper activity provided by Ly-1- and Ig-bearing B cells called BH. The ability of these BH cells to perform this idiotype-specific, genetically controlled helper function is related to the NPb idiotype specificity of their cell surface receptors. However, the means by which BH cells communicate with and stimulate NPb idiotypic B cell subsets is unknown. In this paper, an Ly-1- and immunoglobulin-bearing B helper cell hybridoma is described. Supernatants from the hybridoma or its subclones were shown to specifically help the response of NPb idiotypic PFC to NP-Ficoll when added to responder cell cultures depleted of Thy-1 and Ly-1 regulatory cell populations. Under these experimental conditions hybridoma supernatants functioned in much the same fashion as populations of Ly-1- and Ig-bearing BH helper populations described previously. NPb idiotype-specific helper activity was mediated by two separable activities elaborated by the hybridoma, an anti-NPb idiotype antibody and a non-Ig (lymphokine) activity. It was shown that both the Ig and the lymphokine components were required for helper activity. Kinetics experiments showed that the anti-idiotype antibody must be added early in the response to NP-Ficoll, whereas the lymphokine fraction could be added at least as late as day 3 of a 4-day culture in order to observe NPb idiotype-specific help. The data suggest that Ly-1 B cell hybridomas may affect the responsiveness of B cell subsets initially by interaction of anti-idiotype antibody with NPb idiotypic B cell surface receptors, followed by growth or maturation signals mediated by non-Ig lymphokine(s). The possibility that the helper activity of these Ly-1 B cell hybridomas represents the combined effects of an idiotype-specific network system and nonspecific growth or maturation factor activity in direct B cell-B cell interactions is discussed.