Antigen-presenting cells and granulocytes are also present within the ILT and ALT. Representative deconvolved confocal images of adult zebrafish gills displaying the ILT (A, C, E, G) and the ALT (B, D, F, H) at high-magnification, as illustrated on panel (I). Images were acquired from 30 μm whole-body cryosections. Cryosection showing the ILT (A) and ALT (B) of mhc2:GFP (cyan hot) zebrafish stained with DAPI (red) reveal numerous mhc2 expressing cells. Purple arrowheads point to GFP positives pavement cells, green arrowheads highlight GFP low reticulated epithelial cells and yellow arrows indicate the presence of large GFP positive cells. (C, D) Cryosections from mhc2:GFP (green) zebrafish gills, stained with fluorescent peanut agglutinin lectins (red) and DAPI (blue), show the presence of dendritic cells among the ILT and ALT (cyan arrowheads), and the presence of small GFP+ cells displaying a lymphocyte-like morphology (cyan stars). To note, the peanut agglutinin lectin also binds to the surface of some pavement cells (magenta arrows). (E, F) Cryosections from mfap4:mCherry-F zebrafish, whose macrophages are fluorescent, stained with phalloidin (green) and DAPI (blue), identify the presence of many macrophages (red hot) within the ILT and ALT (cyan arrows). (G, H) Cryosections from mpx:GFP zebrafish, whose neutrophils are fluorescent, stained with phalloidin (green) and DAPI (blue), identify the presence of neutrophils (red hot) within the ILT and ALT (red arrows). Images are maximum intensity projections: 2 µm (A–D, G, H), 4 µm (F) and 9 µm (E). Annotations: Aa, Afferent artery; ALT, Amphibranchial Lymphoid Tissue; Bc, Branchial cavity; C, Cartilage; Ea, Efferent artery; Ga, Gill arch; ILT, Interbranchial Lymphoid Tissue; La, Lamella; Rbc, Red blood cells; Rc, Rodlet cells and Vb, Vascular bleb. Scale bars: 10 µm (A–D, H), 20 μm (F, G) and 40 µm (E).
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