Contributed Papers: Oral Presentations Immunology |
Proteins from
the wall-forming bodies of Eimeria maxima: function
and immunogenicity
Smith, N.C.1, Belli,
S.I.1, Katrib, M.1, Witcombe, D.M.1, Mai, K., Skene,
C.1, Gleeson, M.T.1, Wallach, M.G.1, Ferguson, D.J.P.2,
Luxford, C.3, Davies, M.3 and Finger, A.4
1Institute for the Biotechnology
of Infectious Diseases, University of Technology,
Sydney, Australia; 2Nuffield Department of Pathology,
University of Oxford, UK; 3The Heart Research Institute,
Sydney, Australia; 4Abic Veterinary Products Ltd,
Netanya, Israel.
Wall-forming
bodies type 1 of Eimeria maxima are large, electron-dense
vacuoles that stain positively with antibodies in
an enriched preparation of native forms of 56, 82
and 230 kDa gametocyte proteins (APGA). Wall-forming
bodies type 2 also react positively with these antibodies,
but are less electron-dense than wall-forming bodies
type 1, have whorled or donut-shaped profiles and
remain enclosed in the rough endoplasmic reticulum.
At the initiation of oocyst wall formation, wall-forming
bodies type 1 first align at the periphery of the
macrogamete, then release their contents to form an
electron-dense outer oocyst wall that reacts with
anti-APGA antibodies. Wall-forming bodies type 2 subsequently
give rise to an electron-lucent inner wall. Proteomic
and Western blot analysis has revealed that the 56
and 82 kDa proteins are processed into smaller, tyrosine-rich
proteins that can cross-link and harden to form the
oocyst wall of Eimeria maxima. This observation helps
to explain the molecular basis of action of the subunit
vaccine, CoxAbic®, which includes native 56 and
82 kDa proteins and stimulates strong antibody responses
to protect the hatchlings of vaccinated hens from
coccidiosis. Genes encoding these two immunodominat
components of CoxAbic® were cloned and the recombinant
proteins expressed in E. coli and purified. Both recombinant
proteins are immunogenic, eliciting dose-dependent
antibody responses comparable to that provoked by
CoxAbic® and able to recognise the native proteins
in that vaccine. Furthermore, the recombinant proteins
are able to inhibit the binding of anti-APGA antibodies
to APGA, indicating that the recombinant versions
have some promise as components of a second-generation
subunit vaccine against poultry coccidiosis.