Nature of Candida albicans-derived carbohydrate antigen recognized by a monoclonal antibody in patient sera and distribution over Candida species

The minimal epitope of an anti-Candida albicans mannan monoclonal antibody (MAb) EB-CA1, used to detect mannanemia in patient sera, was determined. MAb EB-CA1 exhibited reactivity with oligomannosides released from the mannan acid stable domain, converted into neoglycolipids (NGLs) and coated onto ELISA plates. Reactivity occurred with mannopentaose and higher oligomers, whereas mannotriose and mannotetraose were unreactive. MAb EB-CA1 binding to mannan acid stable mannopentaose NGL displayed a dose dependent and saturable specific reactivity curve whereas there was a complete absence of binding, even at high concentrations, with NGLs constructed from the β-1,2-linked mannopentaose derived from the mannan acid labile fraction. MAb EB-CA1 binding to acid stable mannopentaose NGL was inhibited by the homologous oligomannoside but not by mannotriose and mannotetraose. NMR analysis showed that mannotriose and mannotetraose contained exclusively α-1,2-linked d-mannopyranose units and that mannopentaose was a mixture of a mannopentaose α-1,2-linked and an isomer in which the fifth mannose was α-1,6-linked to the reducing unit of manno-α-1,2 tetraose. Western blot analysis has shown that MAb EB-CA1 epitope was expressed on a wide range of C. albicans manno-glycoconjugate as well as on manno-glycoconjugates of other pathogenic species of the genus Candida, viz. C. tropicalis, C. glabrata, C. parapsilosis and C. krusei.