Glucuronoxylomannan, galactoxylomannan, and mannoprotein occupy spatially separate and discrete regions in the capsule of Cryptococcus neoformans.

The capsular polysaccharides of Cryptococcus neoformans have historically been divided into three components namely, glucuronoxylomannan (GXM), galactoxylomannan (GalXM), and mannoprotein (MP) but their relative spatial-geographical relationship in the capsule is unknown.  To explore this problem would require the capacity for visualizing these components in the capsule.  Prior studies have reported serological reagents to GXM and GalXM but no antibodies are available against MPs.  Consequently, we immunized Balb/c mice with C. neoformans recombinant mannoprotein 98 and recovered twelve monoclonal antibodies (mAbs) of which one, an IgG2a designated 18F2, bound to intact cells by immunofluorescence. mAb 18F2 bound to the cell wall surface in acapsular and encapsulated cells.  Using mAb 18F2 and previously generated antibodies to GXM and GalXM we have established the localization of three capsular components GXM, GalXM and one type of mannoprotein, MP98 on the C. neoformans cell.  The results show that MP98, like GalXM, is found near the cell wall and this information allows us to begin to discern the geography of the cryptococcal capsule.