Figure 3. Immunolocalization of MUC21 and MUC22 in the Human Corneal Epithelium and the Human Lacrimal Gland.

An anterior segment isolated from a human donor eye was formalin-fixed within 24-hours post-mortem and paraffin-embedded. A formalin-fixed human lacrimal gland embedded in paraffin was obtained from the Ophthalmic Pathology Laboratory of Tufts Medical Center. Tissues cross-sections were prepared, then processed and indirectly immunostained for MUC21 or MUC22 as described (Itakura et al., 2019). The human MUC21 primary antibody was purchased from Sigma-Aldrich Corp. (St. Louis, MO). It is derived from a rabbit polyclonal antisera raised against a peptide from the human MUC21 cytoplasmic tail (561-CVRNSLSLRN TFNTAVYHPH GLNHGLGPGP GGNHGAPHRP RWSPNWFWRR PVSSIAMEMS GRNS-624), then affinity-purified. The human MUC22 primary antibody was characterized in one of our labs, as described (Hijikata et al., 2011). A rabbit polyclonal antisera produced by GENENET (Fukuoka, Japan) was raised against a peptide (TPTNVIKPSGYLQP) from the human MUC22 stem region located just before the transmembrane domain, then affinity-purified. A 3,3′-diaminobenzidine (DAB) chromogen kit was used to detect secondary antibody binding (Vector Laboratories, Burlingame, CA). The negative control (Neg. control) omitted the primary antibody. Sections were counterstained with hematoxylin. A-C) Cross-sections through the anterior segment focusing on immunostaining results (brown color) in the cornea epithelium. The hematoxylin counterstain is dark blue. Magnification = 40X. D-L) Cross-sections through the lacrimal showing immunostaining results (brown color). The hematoxylin counterstain is dark blue. D-F) Low magnification view (10X); G-I) Higher magnification (40X) focusing on a lacrimal duct; J-L) Higher magnification focusing on serous acini. These experimental findings have not been previously published.