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Degradation of Uniquely Glycosylated Secretory Immunoglobulin A in Tears from Patients with Pseudomonas aeruginosa Keratitis

From the Institute of Medical Microbiology and Immunology, Aarhus University, Aarhus, Denmark; and the Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark.

PURPOSE. To investigate the integrity of secretory (S)-IgA in tear fluid during bacterial keratitis and to evaluate the significance of specific Pseudomonas aeruginosa extracellular proteases in the observed degradation of S-IgA.

METHODS. The integrity of component chains of S-IgA in tear fluid from patients with keratitis caused by P. aeruginosa, Streptococcus group G, Moraxella catarrhalis, Staphylococcus aureus, coagulase-negative staphylococci, and the IgA1 protease–producing Streptococcus pneumoniae were compared with S-IgA in tear fluid, colostrum, and saliva from healthy individuals and with tear S-IgA incubated with clinical isolates and genetically engineered P. aeruginosa strains with different protease profiles. Degradation of S-IgA and the significance of its glycosylation were analyzed in Western blot analysis developed with antibodies against individual chains of S-IgA.

RESULTS. Secretory component (SC) of S-IgA secreted by the lacrimal glands was more abundantly glycosylated than SC in colostrum and saliva. S-IgA degradation was observed only in tears from P. aeruginosa–infected patients, in a pattern similar to that observed in incubation of tear samples with P. aeruginosa strains and to an extent closely correlated with their expression and activity of individual proteases. Experiments using isogenic mutants of P. aeruginosa PAO1 lacking either elastase or alkaline protease indicated that several proteases were working in concert.

CONCLUSIONS. Surprisingly, SC of tear S-IgA is more abundantly glycosylated than SC of S-IgA in other secretions, a difference of potentially great functional significance. Primarily, SC and -chains are partially degraded in vivo during Pseudomonas keratitis by the concerted action of several proteases, including elastase and alkaline protease.

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