Characterisation of Apical Membrane Antigens in Eimeria tenella

Karen Billington1, David Ferguson2 and Fiona Tomley1
1Institute for Animal Health, Compton. 2John Radcliffe Hospital, Oxford

 

Apical membrane antigen 1 (AMA-1) was first identified within the blood stages of Plasmodium knowlesi as a target of invasion inhibitory monoclonal antibodies and homologous proteins are conserved in other species of malaria parasites and in Toxoplasma gondii. AMA-1 is a transmembrane protein that is secreted from the microneme organelles during invasion onto the parasite surface from where it is proteolytically cleaved by a muti-functional membrane-bound serine proteinase that is also responsible for the shedding of other parasite surface molecules.

We have identified two Eimeria tenella homologues of AMA-1 with all the characteristic hallmarks of the AMA-1 family including N-terminal signal peptides, extracellular domains organised around 16 conserved cysteines and C-terminal transmembrane and cytoplasmic domains. EtAMA-1 is expressed exclusively within the sporozoite stage of the parasite and EtAMA-2 is expressed only within the merozoite stages. Further studies to examine the secretion and processing of these molecules are underway.