Characterization of Cryptococcus neoformans capsular glucuronoxylomannan polysaccharide with monoclonal antibodies

Mice were immunized with Cryptococcus neoformans serotype A capsular glucuronoxylomannan (GXM) conjugated to bovine serum albumin-adipic dihydrazide. Two splenocyte fusions yielded two monoclonal antibodies (MAbs) that were highly reactive in dot enzyme immunoassay, immunofluorescence, and sandwich enzyme immunoassay. The first MAb, BD-1 [immunoglobulin G1 (kappa) [IgG1(kappa)]], was GXM-A and GXM-D specific, whereas the second MAb, BA-4 (IgM), reacted with GXM-A and GXM-B. A third MAb, CD-6 [IgG1(kappa)], originated from mice immunized with O-deacetylated GXM-C-bovine serum albumin and reacted with GXMs of all four serotypes. Two of the MAbs (CD-6 and BD-1) were further characterized with chemically modified GXMs. Removal of glucuronosyl residues completely inhibited the binding of both MAbs, implicating (1----2)-beta-glucuronic acid as a key component of the epitope. Removal of (1----2)-beta-xylosyl residues decreased reactivity to an intermediate extent. O deacetylation led to a measurable decrease but had the least inhibitory effect of the three GXM derivatives tested. The combining site for these two MAbs appears to be a complex antigenic determinant involving more than one glycosidic residue.