GENERATION OF BIOLOGICALLY-ACTIVE ANTI-CRYPTOCOCCUS NEOFORMANS IGG, IGE AND IGA ISOTYPE SWITCH VARIANT ANTIBODIES BY ACRIDINE-ORANGE MUTAGENESIS

Administration of MoAbs to Cryptococcus neoformans capsular glucuronox ylomannan (GXM) call alter the course of infection in mouse models. Ho wever, the effectiveness of these antibodies appears to depend on isot ype and specificity. Comparison of isotype protection efficacy require s families of MoAbs with identical fine specificity and different cons tant region domain. The generation of such families by hybridoma techn ology is not always possible because the immune response produces MoAb s of limited classes or subclasses. In these instances isotype switch variants can be isolated in vitro. Unfortunately, standard methods of recovering spontaneous switch variants are often unsuccessful, mainly because of the low frequency of switching. In this study we demonstrat e that acridine orange stimulation of an IgG3 anti-C. neoformans-produ cing hybridoma can be used to recover the entire set of isotype switch variants: IgG1, IgG2b, IgG2a, IgE and IgA. All isotype switch variant s bind to GXM; fine specificity mapping, using an 11 amino acid peptid e polysaccharide mimetope. revealed conservation of binding site speci ficity. Furthermore, all isotype switch variants reacted with an anti- idiotopic MoAb. The functional activity of this set of MoAbs was demon strated by their ability to enhance phagocytosis and antifungal effica cy of human human macrophage-like THP-1 cells, with IgG3 being the mos t effective and IgE being the least effective.