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E. Knop, P. Claus, N. Knop; Eye-associated Lymphoid Tissue (EALT): RT-PCR Verifies the Presence of mRNA for IgA and its Transporter (Secretory Component) in the Normal Human Conjunctiva . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3801.
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Purpose: In a previous study we showed in a large number of normal human tissues that the conjunctiva regularly contains a mucosal immune system with lymphocytes and plasma cells. Immunohistochemistry indicated that the plasma cells were positive for IgA while its transporter molecule secretory component (SC) was located inside the overlying epithelial cells. However, there was concern about the identity of the immune staining. Therefore it was attempted to show the presence of the respective mRNAs by RT-PCR. Methods: Tissue of the conjunctiva and the lacrimal gland was taken from six randomly chosen macroscopically normal eyes of body donors admitted to the department of anatomy. Primers for IgA and SC mRNA were constructed according to sequence data from the NCBI database and reverse transcriptase (RT-) PCR was performed with standard reagents. Results: All normal tissues of the conjunctiva as well as the lacrimal gland showed the presence of a single broad band of RT-PCR products of the expected size equivalent to each of the chosen sequences for IgA and SC transcripts. Lacrimal gland tissue with the known presence of IgA-producing plasma cells and secretory component served as a positive control. In muscle tissue, which was used as a negative control, the respective RT-PCR products were absent while the RT-PCR product for GAPDH (a house-keeping enzyme) was still present as expected. Conclusions: These results support the previous immunohistochemical findings of IgA and SC proteins in the normal human conjunctiva and verify the presence of mRNA for IgA and SC. The normal ocular surface hence produces these proteins locally. The conjunctiva is therefore a component of the ocular surface secretory immune system. It can act in concert with the lacrimal gland and the lacrimal drainage system that together form an eye associated lymphoid tissue (EALT) as a functional unit for ocular surface immune protection.
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