Cryptosporidium parvum sporozoite pellicle antigen recognized by a neutralizing monoclonal antibody is a beta-mannosylated glycolipid

The protozoan parasite Cryptosporidium parvum is an important cause of diar rhea in humans, calves, and other mammals worldwide. No approved vaccines o r parasite-specific drugs are currently available for the control of crypto sporidiosis. To effectively immunize against C. parvum, identification and characterization of protective antigens are required. We previously identif ied CPS-500, a conserved, neutralization-sensitive antigen of C. parvum spo rozoites and merozoites defined by monoclonal antibody 18.44. In the presen t study, the biochemical characteristics and subcellular location of CPS-50 0 were determined. CPS-500 was chloroform extractable and eluted with aceto ne and methanol in silicic acid chromatography, consistent with being a pol ar glycolipid, Following chloroform extraction and silicic acid chromatogra phy, CPS-500 was isolated by high-pressure liquid chromatography for glycos yl analysis, which indicated the presence of mannose and inositol, To ident ify which component of CPS-500 comprised the neutralization-sensitive epito pe recognized by 18.44, the ability of the monoclonal antibody to bind CPS- 500 treated with proteases, or with alpha- or beta-glycosidases, was determ ined. Monoclonal antibody 18.44 did not bind antigen treated with beta-D-ma nnosidase but did bind antigen treated with alpha-D-mannosidase, other alph a- or beta-glycosidases, or a panel of proteases, These data indicated that the target epitope was dependent on terminal beta-D-mannopyranosyl residue s. By immunoelectron microscopy, 18.44 binding was localized to the pellicl e and an intracytoplasmic tubulovesicular network in sporozoites, Monoclona l antibody 18.44 also bound to antigen deposited and released onto substrat e over the course travelled by gliding sporozoites and merozoites. Surface localization, adhesion and release during locomotion, and neutralization se nsitivity suggest that CPS-500 may be involved in motility and invasion pro cesses of the infective zoite stages.