title: M cell-targeted ocular immunization: effect on immunoglobulins in tears, feces, and serum.
abstract: OBJECTIVE
  This study investigates whether antigen-sampling M cells, present in the follicle-associated epithelium (FAE) above organized conjunctiva-associated lymphoid tissue in rabbits, bind and retro-transport secretory IgA (sIgA) from the tear film. The hypothesis that IgA-mediated uptake of antigens promotes local and systemic production of immunoglobulins was tested.
  
  
  METHODS
  sIgA binding and retro-translocation by M cells was characterized by immunocytochemistry. Immunoglobulin concentrations in tears, feces and serum were measured using enzyme-linked immunoassays (ELISA) after topical and systemic immunization with either goat IgG anti-rabbit IgA or nonspecific goat IgG.
  
  
  RESULTS
  Endogenous sIgA was found associated with the apical membrane of conjunctival M cells. Exogenous anti-IgA immunoglobulins were translocated across M cells. Significant levels of sIgA against goat IgG were present in tears of pre-immune animals. Topical application of either goat IgG specific for rabbit IgA or nonspecific goat IgG led to similar increases in antigen-specific IgA in tear, feces, and serum. The antigen-specific IgG response in tears mirrored the serum response for both immunogens consistent with transudation of this immunoglobulin. The IgM response in tears and serum was weak for both immunogens. Systemic immunization did not sustain or enhance the local mucosal IgA responses.
  
  
  CONCLUSIONS
  Conjunctival M cells bind and translocate sIgA from the tear film. Topical conjunctival immunization leads to generation of antigen-specific immunoglobulins from both local and distant mucosae and in serum. Natural antibodies, present in the tear film before immunization, may have contributed to similar immune responses to goat anti-rabbit IgA and nonspecific goat IgG.
authors.affiliation: Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211-7400, USA. phillipst@missouri.edu
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Phillips
authors.forename: Jeremy
authors.initials: J
authors.lastname: Sharp
authors.forename: Kay
authors.initials: K
authors.lastname: Rodgers
authors.forename: Hongshan
authors.initials: H
authors.lastname: Liu
mesh_terms: D000818:Animals; D000941:Antigens / Q000276:immunology*; D003228:Conjunctiva / Q000276:immunology* / Q000648:ultrastructure; D004797:Enzyme-Linked Immunosorbent Assay; D005243:Feces; D005260:Female; D007114:Immunization; D007071:Immunoglobulin A, Secretory / Q000032:analysis* / Q000097:blood*; D007074:Immunoglobulin G / Q000276:immunology*; D007075:Immunoglobulin M / Q000276:immunology*; D008221:Lymphoid Tissue / Q000276:immunology; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009092:Mucous Membrane / Q000166:cytology / Q000276:immunology*; D011817:Rabbits; D013666:Tears / Q000276:immunology*
chemical_list: D000941:Antigens; D007071:Immunoglobulin A, Secretory; D007074:Immunoglobulin G; D007075:Immunoglobulin M