Fig. 5.

Details of the asexual multiplication of Eimeria tenella in the chicken caecum observed in plastic sections after staining with azure A (a, d, g, l and p), after immunoperoxidase staining with anti-EtENR (b, e and h) and double labelling with anti-EtENR (green) and anti-EtMIC2 (red) (c and f) or anti-EtSAG4 (red) (i, m, n, o and q). Scale bars = 1 μm (a–f, j and k), 5 μm (g–i) and 10 μm (l–q). (a–c) Early stage of newly entered merozoites showing two small apicoplasts (arrowheads) with some residual anti-EtMIC2 staining (red). (d–f) Early growth stage in which there is marked expansion of the size and signal from the apicoplasts (A). (g–i) Mid-stage with repeated nuclear division resulting in numerous nuclei. Note the increased number of large pleiomorphic-shaped EtENR positive apicoplasts (A). (j) Deconvoluted enlargement of the enclosed area in m showing the donut and crescentic shape of the large apicoplasts. (k) Deconvoluted enlargement of the enclosed area in n showing repeated constrictions (arrowheads) along the enlarged apicoplasts and the formation of small spherical apicoplasts. (l) Late schizont with numerous nuclei (N) and deep invaginations of the plasmalemma (arrows) increasing the surface area of the schizont. (m) Similar stage to that in l showing a number of randomly distributed large apicoplasts (green). N – nucleus. (n) Slightly later stage than in m showing the apicoplasts as elongated structures with a bead-like appearance and numerous small apicoplasts. The surface of the schizont is still negative for EtSAG4 at this stage. N – nucleus. (o) Late stage in schizogony showing the initiation of daughter formation identified by EtSAG4 positivity (red) at the schizont surface. Note the nuclei (N) and small apicoplasts (A) have become peripherally located. (p) Mature schizont consisting of numerous fully formed merozoites (Me). (q) Mature schizont showing the fully formed merozoites (Me) outline by the EtSAG4 staining (red) and containing one to three small apicoplasts (A).