Ocular Surface Inflammation Induced by Propionibacterium acnes

Purpose. In the eye, Propionibacterium acnes is commonly isolated in the lid, conjunctiva, and meibomian gland secretion. Well known as a causative bacterium of granulomatous endophthalmitis and a potent inflammatory stimulus, P. acnes reportedly induces a delayed-type hypersensitivity (DTH) response and forms granulomas in the liver and lung in animal models. In this study, we examined whether P. acnes can induce a DTH response in the cornea. Methods. Six- to 8-week-old female Lewis rats were immunized with heat-killed suspension of P. acnes and assessed as to DTH response via ear challenge at 2 weeks after immunization. At 3 weeks after immunization, P. acnes suspension was injected in the rat corneal stroma, which was then observed biomicroscopically at 6, 24, and 48 hours after injection. Phenol-killed Staphylococcus aureus suspension was also used for the comparison. Histological examination was also performed on the corneal tissues, using hematoxylin and eosin staining as well as immunohistochemical staining against CD4 and CD8 T cells. Results. Rats immunized with P. acnes suspension showed significantly higher ear swelling values at both the 24- and 48-hour measurements than did the naïve controls (p < 0.005). Massive cellular infiltration with stromal edema was observed biomicroscopically at 48 hours after injection of P. acnes suspension in the corneal stroma. Histological study showed that the cell infiltration pattern was similar to that of DTH in the skin, i.e., neutrophils infiltrated at 6 hours, followed by mononuclear cells that, including macrophages and lymphocytes, increased and mixed with neutrophils, accompanied by stromal edema at 48 hours. Immunohistochemical study revealed that CD4 T-cell infiltration in the corneal stroma appeared to predominate over CD8 T-cell infiltration. Conclusions. These results indicate that P. acnes can induce a DTH response in the cornea and may be a causative bacterium of ocular surface inflammation.