The Macrophage Inhibitory Factor of Eimeria species
Miska, KB., Lillehoj, HS., Allen, PA., Fetterer, RH, and Jenkins,
MC.
USDA/ARS, Animal Parasitic Diseases Laboratory
10300 Baltimore Ave, Beltsville, MD 20705 U.S.A
Development of drug resistance and the paucity of new
chemotherapeutic agents have increased the need for new drugs as well as vaccine
targets against poultry coccidiosis. One approach used in identifying novel
targets is the random screening of transcripts expressed during the invasive
stages of the parasite life cycle. While screening a cDNA library derived from
merozoites of Eimeria acervulina a single full-length clone was isolated, and
this shared between 35-38% amino acid identities with the Macrophage Inhibitory
Factors (MIFs) of vertebrates. To further characterize Eimeria MIF the
full-length Eimeria tenella cDNA was also cloned and sequenced. The amino acid
identity between the two Eimeria MIFs is 64%. The mRNA expression pattern of
Eimeria MIF was determined using quantitative RT-PCR on RNA collected from
several stages of the parasite life cycle. MIF expression profiles in both E.
acervulina and E. tenella were found to be almost identical, with high levels of
transcripts present in merozoites, while developing oocysts and sporozoites
expressed only small amounts of MIF mRNA. Using Western analysis, a 12 kDa
protein, corresponding to the molecular weight of MIF, was shown to be highly
expressed in merozoites, while expression in other stages were significantly
lower. It also appears that MIF is secreted by E. acervulina merozoites. The
amount of secreted MIF is increased proportionately with the temperature in
which merozoites were incubated. Because Eimeria MIF is strongly associated with
merozoites its potential as a vaccine candidate should be evaluated in the
future.