Reactivity patterns and epitope specificities of anti-Cryptococcus neoformans monoclonal antibodies by enzyme-linked immunosorbent assay and dot enzyme assay

Abstract

Cryptococcus neoformans glucuronoxylomannans (GXM) are capsular polysaccharides important for virulence in cryptococcosis. This study used dot enzyme assays (DEA) and enzyme-linked immunosorbent assays (ELISA) to determine the reactivity patterns of 21 murine monoclonal antibodies (MAbs) with structurally defined GXMs from five serotypes. The MAbs were categorized into eight groups on the basis of DEA and five groups on the basis of ELISA. MAbs 302, 339, and 439 were studied extensively for their binding to various native and chemically modified GXMs. Quantitative variation in the inhibitory effects of GXMs on the binding of MAbs 302, 339, and 439 were observed by competitive ELISA. O-Deacetylation of serotype A, B, and D GXM resulted in the complete loss of their inhibitory properties. Carboxyl group reduction of GXMs from serotypes A and D resulted in a significant decrease of inhibitory activity for MAb. Xylomannans and methyl glycosides exhibited no detectable inhibitory activity on MAb binding to GXM. The results indicate (i) the existence of five to eight MAb-defined distinct epitopes in C. neoformans GXM that can elicit antibody responses, (ii) MAb detection of antigenic variation within GXMs assigned to a particular serotype, (iii) good correspondence between the patterns of MAb reactivities and polyclonal rabbit factor sera, (iv) good agreement between MAb molecular structure and serotype reactivity, and (v) a dependence of the serotype reactivity profile for a given MAb on the technique used to measure binding.