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.