The expression of a set of antibody variable regions in lipopolysaccharide-reactive B cells at various stages of ontogeny and its control by anti-idiotypic antibody

Abstract

An analysis is presented in which we measure the expression of a subset of antibody variable (V) regions in lipopolysaccharide (LPS)-reactive precursor B cells at various stages of ontogeny. The V regions were characterized by hapten (4-hydroxy-3-nitrophenyl)acetyl (NP)-binding specifity and/or expression of idiotypic determinants whose genetic basis had been explored in previous studies. Only V regions containing the V lambda 1 domain were considered: this allowed an unequivocal determination of idiotopes and reduced heterogeneity in the system essentially to the multiplicity of VH and D genes. It was found that approximately every fourth lambda 1-bearing LPS-reactive splenic B cell produces an NP-binding antibody. Approximately 1 in 40 lambda 1-bearing cells expressed an idiotope (Ac38) which is encoded by V lambda 1 and a set of related VH genes in combination with D and J elements. Of these cells, only a minority produce an NP-binding antibody and a few percent of the latter express a second idiotope (Ac146) which is known to be restricted to a subset of Ac38-positive, NP-binding humoral antibodies. All these frequencies are in good accord with previous analyses of anti-idiotope-induced antibodies in the serum. They can be easily accommodated into a simple model of random selection of VH genes in LPS-reactive B lymphocytes. The frequencies of the V regions under study were essentially the same in LPS-reactive B cells from spleens of adult and newborn animals and in LPS-reactive B cells generated from bone marrow pre-B cells in vitro. In the case of the latter cells the frequencies were independent of the absence or presence of T cells in the culture system. While we could thus detect, in naive mice, neither positive nor negative selection of the cells from the time of their generation in the bone marrow until their arrival in the periphery, negative selection is in principle possible: the presence of microgram amounts of anti-idiotope antibodies during maturation from pre-B to B cells specifically blocks the appearance of idiotope-bearing LPS-reactive cells in vitro. The potential physiological role of the latter effect in the sense of self-stabilization of the expressed antibody repertoire in ongoing immune responses and the possibility that frequency determinations in LPS-reactive B cells may be not representative for the repertoire expressed in the population of mature B cells is discussed.