Immunomorphological and morphological analysis of the salmonid ILT, with the lumen of the branchial chamber indicated (lu). (A) Abundant CD3ε+ (red) cells between the interbranchial septum (is) and the lumen of the branchial chamber. (B) Polarized cells attached to the basal membrane (arrowheads) covered by CD3ε+ (red) cells. (C) Towards the lumen (lu) of the branchial chamber, CD3ε+ cells are more scattered and are covered by an epithelial cell layer containing goblet cells (arrowhead). (D) Strong CD3ε staining (green) of the ILT located between the basal membrane (arrowhead) and the branchial lumen (lu). PI counterstaining in red. (E) Staining for cytokeratin (green) reveals a meshwork of interstitial cells. (F) CD3ε+ cells (green) embedded in the meshwork of cytokeratin+ cells (red) of the interstitium. (G) Very few Ig+ cells (green) are present in the ILT. PI counterstaining in red. Scale bars: A = 200 μm, B,C = 40 μm, D,E,G = 80 μm, F = 60 μm.