CD28 Costimulation Is Required for Development of Herpetic Stromal Keratitis but Does Not Prevent Establishment of Latency

Abstract

Corneal infection with herpes simplex virus 1 (HSV-1) leads to infection of trigeminal ganglia (TG), typically followed by the establishment of latency in the infected neurons. When latency is disrupted, the virus reactivates and migrates back to the cornea, where it restimulates the immune response, leading to lesions in a disease called herpetic stromal keratitis (HSK). HSK requires T cell activation, as in the absence of T cells there is no disease. We decided to determine if CD28 costimulation of T cells was required in HSK. The results indicated that C57BL/6 CD28−/− and BALB/c CD28−/− mice failed to develop recurrent HSK, while their wild-type counterparts did. In order to better understand the dynamics of TG infection in these mice, we evaluated the amount of virus in infected TG and the number of individual neurons harboring latent virus. The results indicated that CD28−/− mice possessed significantly increased genome levels in their TG but many fewer LAT-positive cells than wild-type mice from day 7 to day 30 but that after day 30 these differences became nonsignificant. We next evaluated total and antigen-specific CD8+ T cells in TG. The results indicated that there were significantly fewer CD8 T cells in TG from day 10 to day 25 but that after that the differences were not significant. Taken together, these data suggest that CD28 costimulation is required for HSK but that while initial infection of TG is greater in CD28−/− mice, this begins to normalize with time and this normalization is concurrent with the delayed development of antigen-specific CD8+ T cells. IMPORTANCE We study the pathogenesis of herpes simplex virus-mediated corneal disease. T cells play a critical role both in disease and in the maintenance of latency in neurons. Consequently, the focus of this study was to evaluate the role that T cell costimulation plays both in corneal disease and in controlling the ability of the virus to maintain a stable infection of the ganglia that innervate the cornea. We demonstrate that in the absence of costimulation with CD28, corneal disease does not take place. However, this costimulation does not prevent the ability of CD8+ T cells to develop and, thus, control latent infection of neurons. We conclude from these studies that CD28 costimulation is required for corneal destructive immune responses but that CD8+ T cells develop over time and help to maintain latency.

Local Immune Control of Latent Herpes Simplex Virus Type 1 in Ganglia of Mice and Man

“…These stressors not only suppress the immune system, but they also correlate with a loss of control of viral latency. This comes in the form of increased viral genomic DNA within the TG and a modest production and release of infectious virus (14,(165)(166)(167)(168)(169). Together, these data suggest that loss of viral control is a direct effect of immunosuppression.…”

“…B-cell deficiency during early infection can lead to viral dissemination to the brain, encephalitis and mortality ( 179 , 180 ). Serum antibodies are effective at controlling early viral replication of highly pathogenic HSV-1 strains like McKrae or SC16 ( 167 ). While serum antibodies have not been tested in less pathogenic models of disease, recent studies have shown how maternal antibodies prevent disease and morbidity in neonatal HSV infections ( 181 , 182 ), which illustrates a potential role that circulating antibodies play in the prevention of disseminated disease.…”

Absence of CD28-CTLA4-PD-L1 Costimulatory Molecules Reduces Herpes Simplex Virus 1 Reactivation

“…CXCL10 is a ligand for the chemokine receptor CXCR3, which is highly expressed on activated T cells and is associated with recruitment of T cells to sites of inflammation. Downregulation of CXCL10 is a major indicator of impaired T cell migration to the site of inflammation ( 59 ). This could be further explained based on the enhanced T cell exhaustion (PD1) in TG of knockout mice in our study, which in turn interferes with T cell activation and function, as we have shown previously ( 21 ).…”

CD137 costimulation is associated with reduced herpetic stromal keratitis and with developing normal CD8+ T cells in trigeminal ganglia

“…Mice were reactivated from latency as previously described [21,22]. Briefly, the eyes of all latently infected mice were examined for corneal opacity prior to UV-B irradiation, and only animals with clear corneas were used, and mice with residual corneal disease from the primary infection are removed from the study.…”

“…Stromal opacification was rated on a scale of from 0 to 4, where 0 indicates clear stroma, 1 indicates mild stromal opacification, 2 indicates moderate opacity with discernible iris features, 3 indicates dense opacity with the loss of defined iris detail except pupil margins, and four indicates total opacity with no posterior view. Corneal neovascularization was evaluated as described previously [21,22] using a scale of from 0 to 8, where each of the four quadrants of the eye is evaluated for the density of vessels that have grown into them. Periocular disease was measured in a masked fashion on a semiquantitative scale as previously described [39].…”