Purpose: Secretory IgA (SIgA) is a critical local defense mechanism of mucosal immunity. Although the conjunctiva, as part of the ocular surface, has a mucosa-associated lymphoid tissue, the production of SIgA by local plasma cells and its transport is unequivocally accepted to occur only in the upstream lacrimal gland (LG). The molecular components were therefore investigated by immunohistochemistry (IHC) and their local production verified by RT-PCR.
Methods: Tissues from 18 conjunctivas and 9 LGs of human donor eyes with normal ocular surfaces were analyzed by histology and IHC. Different zones of 12 further conjunctivas and LG tissues were analyzed by RT-PCR for the presence of the respective mRNA.
Results: Plasma cells were present in the diffuse lymphoid tissue of all investigated specimens and showed an intense immunoreactivity for IgA. This immunoreactivity was absent when the antiserum was preadsorbed with the protein. The luminal epithelium, with the exception of goblet and basal cells, was strongly positive for the epithelial transporter molecule secretory component (SC) in the conjunctiva and interconnecting excretory duct similar to the LG. PCR products for IgA, the monomeric IgA-joining molecule (J-chain) and SC were regularly found in all conjunctival zones and in the LG in gel electrophoresis and were sequenced.
Conclusions: The local production of SIgA is for the first time verified by RT-PCR in the human conjunctiva and in the LG. This finding points to an active role of the conjunctiva in secretory immune protection of the ocular surface and supports the presence and importance of EALT at the normal ocular surface.