Characterization of superantigen-induced clonal deletion with a novel clanIII-restricted avian monoclonal antibody: Exploiting evolutionary distanceto create antibodies specific for a conserved V-H region surface

Evolution of the Ab system has yielded three clam of V-H region genes that are represented in almost every known higher species with an adaptive immun e system. These clans are defined by sequence homologies primarily in highl y conserved framework (FR) subdomains, which serve a scaffolding function m aintaining the conformation of loops responsible for Ag binding. Structural analyses indicate that the V(H)F1 and FR3 form a conserved composite expos ed surface, which has been implicated in interactions with B cell superanti gens. To directly investigate the expression of dan-defined supraclonal set s, we exploited the evolutionary distance of the chicken immune system and the selection power of phage display, to derive Abs diagnostic for clan III Ig. Using a specially tailored immunization and selection strategy, we cre ated recombinant avian single chain Fv Abs specific for the clan III produc ts, including those from the human V(H)3 family, and the analogous murine 7 183, S107, J606, X24, and DNA4 families, and binding was competitive with n atural B cell superantigens, The archetype, LJ-26, was demonstrated to reco gnize a clan-specific surface expressed in diverse mammalian, and also the Xenopus and chicken, immune systems. In flow-cytometric studies with LJ-26, we found that treatment of heterozygous T15i transgenic mice with a model B cell superantigen induced a dan m-restricted clonal deletion. These studi es demonstrate the utility of a novel recombinant serologic reagent to stud y the composition of the B cell compartment and also the consequences of B cell superantigen exposure.