IDENTIFICATION OF A DEVELOPMENTALLY-REGULATED SIALIDASE IN EIMERIA-TENELLA THAT IS IMMUNOLOGICALLY RELATED TO THE TRYPANOSOMA-CRUZI ENZYME

Sporozoites and merozoites of three species of Eimeria, E. tenella, E. maxima, and E. necatrix, that cause diarrhea in chickens worldwide, w ere examined for their expression of sialidase (SA) activity. The enzy me was found in three species, and the activity of merozoites was 10-2 0 times higher than that of sporozoites. The enzyme was resistant to d egradation by proteases that are normally present in the intestine, a site inhabited by the Eimeria parasites, and it was relatively resista nt to heat, with optimum activity being at 40-degrees-C, which is with in the range of temperature in the chicken intestine (40-43-degrees-C) . E. tenella SA was immuniprecipitated by monoclonal and polyclonal an tibodies raised against the Trypanosoma cruzi SA (TCSA), and enzyme ac tivity was neutralized by these antibodies. E. tenella SA was identifi ed by immunoblots as a doublet of molecular weight 190000 and 180000 u sing, as a probe, anti-TCSA antibodies and antibodies against a synthe tic peptide (TR) derived from the long tandem repeat domain of TCSA. B inding of the monoclonal and polyclonal antibodies to E. tenella was c ompletely blocked by TR, but not by an irrelevant peptide (BR). Theref ore, E. tenella expresses a developmentally regulated SA that is struc turally related to the T. cruzi counterpart. Because of the high SA ac tivity in merozoites, and by analogy with other SA-producing microbes that inhabit mucin-rich epithelia, we suggest that the Eimeria SA play s a role in desialylating intestinal mucins to reduce viscosity of the local environment and thereby facilitate parasite migration. The enzy me could also play a role in host cell-parasite interaction.