Identification and partial purification of a lectin on the surface of the sporozoite of Cryptosporidium parvum

A human-derived isolate of Cryptosporidium parvum from a symptomatic patient with the acquired immunodeficiency syndrome was expanded in vivo by infecting a neonatal calf with 10⁸ oocysts. Sporozoites were isolated from 4 x 10¹⁰ oocysts harvested from this single infection, and the characteristics of mixed hemagglutination (HA) with rabbit erythrocytes were determined. Sporozoite HA was inhibited by bovine submaxillary mucin (BSM), hog gastric mucin, and orosomucoid, but not by simple sugars, including sialic acid. Carbohydrate-inhibitable HA (lectin) activity increased with sporozoite lysis and was associated with the sporozoite membrane fractions. The ability of intact sporozoites to form rosettes around erythrocytes indicates that the HA (lectin) is, at least in part, present on the parasite surface. Hemagglutination (lectin) activity was partially purified from sporozoite lysates by affinity chromatography with BSM coupled to Sepharose-4B. Best elution was obtained with ethylene glycol and NaCl, which resulted in enrichment of 6 bands compared to the crude starting lysate (Mr = 60, 24, 22, 20, and 15 kDa and a 40-kDa doublet). Our results indicate that an HA (lectin) activity is present on the surface of intact sporozoites where it could play a role in cell-to-cell interactions with eukaryotic targets.