Mechanisms of enhanced corneal graft rejection on clinically uninflamed herpes simplex virus type 1 infected recipient corneal beds

Abstract

Purpose: The frequency of corneal graft rejection is significantly increased on herpes simplex virus type 1 (HSV-1) infected recipient corneal beds, even when recipient corneas lack clinically detectable inflammation at the time of grafting. The purpose of this study was to define mechanisms that promote allograft rejection on these clinically quiet HSV-1 infected corneal beds.

Methods: Wild type (WT) C57BL/6 corneas or those expressing chicken ovalbumin (Ova) as a surrogate alloantigen were transplanted orthotopically to recipient WT C57BL/6 mice. Prior to grafting, recipient mice were mock depleted or depleted of CD4⁺ T cells systemically or locally in the cornea (subconjunctival). Thirty days prior to grafting corneas were mock infected or infected with a 1 x 10⁵ pfu of KOS HSV-1, resulting in corneal epithelial lesions, establishment of latent infections of the trigeminal ganglion, but no corneal inflammation that was clinically detectable at the time of grafting. Quantification of corneal chemokine transcripts by qRT-PCR and leukocytic infiltrates by flow cytometry on dispersed corneal cells was performed before and after grafting.

Results: Prior to grafting, transcripts for chemokines including CXCL10, CXCL9, CCL5, and CCL2 were significantly elevated in infected, but uninflamed recipient corneal beds, and were dramatically reduced by local (corneal) or systemic CD4⁺ T cell depletion. Leukocytic infiltrates were significantly elevated in infected corneal beds prior to grafting and in corneal beds and corneal allografts after grafting, but prior to rejection. The frequency of corneal allograft rejection was significantly increased in infected cornea. Non-immunologic rejection of syngeneic corneal grafts was not significantly increased on HSV-1 infected beds (20% infected vs. 0% non-infected, p > 0.05), but those on infected beds showed significantly increased pathology that did not reach the criterion for rejection.

Conclusions: HSV-1 infected corneas that never develop clinically detectable inflammation nonetheless maintain an inflammatory environment comprised of elevated chemokines and leukocytes for at least 30 days that is regulated by CD4⁺ T cells. This preexisting inflammation predisposes to corneal graft rejection.