Immunopathologic features of Staphylococcus epidermidis-induced endophthalmitis in the rat

Abstract

PURPOSE. To investigate the clinical, histopathologic and immunologic responses to Staphylococcus epidermidis endophthalmitis in a rat model. METHODS. Experimental rats received an intravitreal injection of viable S. epidermidis (7000 organisms), while control rats received sterile saline. The clinical scores, cellular infiltrate in vitreous, and levels of serum and vitreous IgM, IgG and IgA to glycerol teichoic acid (GTA), the major antigenic determinant of S. epidermidis cell wall, were all measured from day 1 to day 30 after injection. RESULTS. The ocular inflammation was largely resolved by day 14. The red reflex was abolished in 50% of rats between days 3 and 10. The bacteria were cleared from the vitreous by day 7. In vitreous, the neutrophils peaked at day 1 and decreased by day 7, and plasma cells were seen between days 1 and 3. Presence of B cells (CD45+/CD3-) was confirmed by flow cytometric analysis of pooled vitreous humor. IgM and IgG but not IgA antibodies to GTA were found in vitreous of injected eyes. The peak of anti-GTA IgM was observed in vitreous of S. epidermidis -infected rats on day 1 and declined by day 7. In contrast to vitreous antibodies, serum anti-GTA IgM antibodies were significantly elevated throughout the course of S. epidermidis endophthalmitis. A weak IgG but no IgA response were observed in serum. Anti-GTA antibodies were also found in low level in normal sera but not in normal vitreous. CONCLUSIONS. The vitreous antibodies may be involved in neutrophil-mediated opsonophagocytosis leading to `spontaneous sterility' of the bacteria, and may play a role in the immuno-pathogenesis of staphylococcal endophthalmitis in the rat.