Secretory IgA inhibits Pseudomonas aeruginosa binding to cornea and protects against keratitis.

PURPOSE

To determine whether secretory IgA (SIgA) antibody inhibits Pseudomonas aeruginosa binding to cornea in vitro and if boosting SIgA antibody in tears using heat-killed P. aeruginosa as an immunizing antigen is protective in vivo in experimentally induced bacterial keratitis in the mouse.

METHODS

SIgA, immunoglobulin-G, immunoglobulin-M, and an undiluted crude human milk preparation were tested in vitro for their ability to inhibit P. aeruginosa binding to the scarified corneas of adult (6 weeks to 6 months of age) mice by topical application of each before similar delivery of the bacterial inoculum. Scanning electron microscopy (scanning EM) was used to quantitate bacterial adherence. In vivo mice were immunized topically with heat-killed P. aeruginosa or sham immunized by application of a similar volume of phosphate-buffered saline (PBS). Tears were collected from both groups of mice and levels of immunoglobulins (Igs) measured by enzyme-linked immunosorbent assay (ELISA). After the second immunization, the same two groups were challenged ocularly with 5.0 x 10(7) colony forming units P. aeruginosa and the response to infection graded.

RESULTS

In vitro, after a 30-minute preincubation with Igs, SIgA (250 micrograms/ml) significantly decreased P. aeruginosa binding to cornea in vitro when compared to the number of bacteria bound in PBS control specimens, and binding reduction was concentration dependent. In vivo, 15 days after a second ocular topical immunization, tear SIgA was elevated significantly and was specific for P. aeruginosa when measured by ELISA. In vivo, corneal disease response grades in the heat-killed antigen immunized mice also were significantly less severe when compared to sham-immunized mice.

CONCLUSIONS

SIgA significantly inhibits binding of P. aeruginosa to the wounded mouse cornea in vitro, and inhibition is concentration dependent. In vivo, specific antipseudomonal SIgA in mouse tears can be elicited by topical ocular immunization with heat-killed P. aeruginosa, and a significant number of immunized animals with elevated levels of SIgA in their tears exhibited less severe ocular disease after bacterial challenge.