Fig.2. Healthy and baculovirus-infected tracheal epithelium and fat body of silkworm larvae. Fourth instar silkworm larvae were infected with 10⁵p.f.u. of RV or WV, or were mock-infected (H₂O injection). At 50h.p.i., when RV-infected insects were fully paralyzed, insect tissues were processed for immunocytochemistry as described in Material and methods. (A) Typical trachea (T) from mock-infected larvae stained with Hematoxylin and Eosin. (B) Typical trachea from mock-infected larvae stained with the AaIT-specific immunoperoxidase (see Materials and methods). (C) Trachea from WV (BmM14)-infected larvae 50h.p.i. Notice the hypertrophied tracheal epithelium (TE) (compared with A and B). (D) Trachea from RV (BmAaIT)-infected and paralyzed larvae expressing AaIT at 50h.p.i. The expressed toxin, indicated by the brown pigmentation, is shown in the cytoplasm of tracheal epithelial cells. The swollen nuclei (TN) are devoid of the toxin. (E) Fat body of WV (BmM14)-infected larvae. Notice the swollen nuclei of the fat body cells (Fbc). (F) Fat body from non-infected larva paralyzed by injection (1.6µg100mg^-1) of AaIT. (G) Fat body from larva 50h.p.i. by the RV, which was incubated with a serum that was quenched with 50µg AaIT for 2h and is devoid of the AaIT-specific antibodies. (H, I) Fat body from RV (BmAaIT)-infected and paralyzed larvae expressing AaIT (arrowheads) at 50h.p.i. Notice the swollen fat body nuclei (FN) that are devoid of toxin staining. Scale bar, 20µm (A–D) and 50µm (E–I).

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