Antigens of Cryptosporidium Sporozoites Recognized by Immune Sera of Infected Animals and Humans

Abstract

The humoral response of humans, calves, and horses to Cryptosporidium sporozoite antigens was evaluated using a western blot technique. Sera from calves, humans, and horses were obtained at various times following the detection of infection. Sera were reacted with detergent-solubilized, sodium dodecyl sulfate polyacrylamide gel-electrophoresed (SDS-PAGE) sporozoite antigens. The number of antigens recognized by immune sera from humans and animals increased with time postinfection. A 20-kDa antigen appears to be a major sporozoite surface determinant labeled via membrane protein biotinylation and recognized by mouse monoclonal antibodies using indirect immunofluorescence and western blotting. Detectable recognition of the 20-kDa band occurred in 3-wk postinfection (PI) sera from all species tested. Reactivity to the 20-kDa band diminished significantly in sera 5 mo PI or longer from infected humans with no known recurrence of cryptosporidial diarrhea. In contrast, 12-mo PI sera from an individual constantly exposed to oocysts under working conditions was as strongly reactive as the 3-wk convalescent sera. Serum reactivity to the 20-kDa antigen appears to be a good indicator of exposure to Cryptosporidium.

Characterization and Formulation of Multiple Epitope-Specific Neutralizing Monoclonal Antibodies for Passive Immunization against Cryptosporidiosis

“…While the mechanism of neutralization by MAb 3H2 has not yet been defined, its recognition of apical complex antigens, including CSL, and the surface pellicle of zoites suggests that it may target the attachment and/or invasion processes as well. The mechanism of neutralization by ␣P23 MAb 1E10 may involve interference with zoite locomotion, because P23 is deposited during gliding motility required in the invasion process (3,10,23). This type of sporozoan motility is characterized by attachment of zoite surface molecules to a substratum, posterior translocation, and forward locomotion (44,45).…”

“…GP25-200 was originally defined by MAb C4A1 as a sporozoite apical and surface pellicle glycoprotein complex comprised of multiple 25-to 200-kDa species identified in reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) (1). P23, a 23-kDa sporozoite surface pellicle protein, was originally identified by MAb C6B6 (1,23). Passive immunization with MAbs C4A1 and C6B6 demonstrated that GP25-200 and P23 each expressed a neutralization-sensitive epitope; however, the efficacy observed was suboptimal (1,42).…”

“…Therefore, effective neutralization of the infective stages could prevent initiation of the life cycle or interrupt and terminate the cycle in an existing infection. The C. parvum antigens GP25-200 (1,39), CSL (39,40), and P23 (1,23) were selected as targets for the present study. Each antigen is involved in the pathogenesis of infection, expressed on the surface of both infective zoite stages, and conserved on diverse C. parvum isolates (1,23,31,39,40).…”

“…The C. parvum antigens GP25-200 (1,39), CSL (39,40), and P23 (1,23) were selected as targets for the present study. Each antigen is involved in the pathogenesis of infection, expressed on the surface of both infective zoite stages, and conserved on diverse C. parvum isolates (1,23,31,39,40). GP25-200 was originally defined by MAb C4A1 as a sporozoite apical and surface pellicle glycoprotein complex comprised of multiple 25-to 200-kDa species identified in reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) (1).…”

Localization of a 23 000 MW antigen of Cryptosporidium by immunoelectron microscopy

“…Because immunocompetent hosts usually recover spontaneously and prove refractive to reinfection, various immunological studies have been performed to identify parasite antigens using immune sera from naturally infected hosts. Immunoblot studies have resulted in the detection of a small molecular weight (MW) antigen (20 000-23 000 MW) in either intact oocyst or sporozoite life cycle stages which is frequently recognized by acute and convalescent sera from humans, goats, cattle and horses (1)(2)(3). However, radiolabelling of intact oocysts with '2^1 failed to locate this antigen on the exterior oocyst wall (2), whereas fluorescent-antibody studies indicated it may be located on the sporozoite and merozoite membranes (3).…”