UVB induced reactivation leads to HSV1 in the corneas of virtually all latently infected mice and requires STING to develop corneal disease

Efficacy of 265 nm ultraviolet C light in the treatment of multi-drug resistant Pseudomonas aeruginosa keratitis in vitro and in an in vivo murine model

BACKGROUND

This study evaluated the in vitro and in vivo efficacy of 265 nanometer (nm) ultraviolet C (UVC) light using 1.93 mW/cm2 against multi-drug-resistant (MDR) Pseudomonas aeruginosa (P. aeruginosa) keratitis.

METHODS

The effect of UVC light was studied on two clinical isolates of P. aeruginosa. Isolate 1 was ciprofloxacin-susceptible, and isolate 2 was MDR (but ceftazidime-susceptible). For the in vitro evaluation, P. aeruginosa isolates (100 μl, 1*108 CFU/ml) were spread on Muller-Hinton solid agar surface and exposed to UVC light for 1, 5, 10, 15, and 30 seconds (s). For the in vivo study, the right eyes of C57BL mice were infected with the P. aeruginosa isolates (5 μL, 1*108 CFU/ml) in two sets with isolates 1 and 2, respectively. The first set (n = 24) was randomized into four groups: a) untreated, b) UVC light 15 s exposure twice daily for two days, c) topical ciprofloxacin 0.3 %w/v twice daily for two days, d) topical ciprofloxacin 0.3 %w/v two-hourly for two days. The second set with MDR P. aeruginosa (n = 24) was treated similarly except for group d (which received topical ceftazidime 5 %w/v two hourly for two days). The left eyes were used to evaluate the safety of applied treatments without inducing infection. At 48 hours (hrs), eyes were enucleated and subjected to microbiological and histopathology analysis.

RESULTS

In vitro, the UVC light exposure resulted in a clear inhibition area for exposures of 15 and 30 s. In the in vivo murine model, UVC light prevented overall clinical severity (p < 0.05) at 24 and 48 hrs by both isolates. Microbiological assessment at 48 hrs showed no growth of organisms in UVC light-treated corneas of either of the sets, similar to an observed treatment with ciprofloxacin (set 1) and ceftazidime (set 2).

CONCLUSION

265 nm UVC light showed an exposure-dependent in vitro bactericidal effect on P. aeruginosa. The in vivo studies showed that UVC light eliminated both strains of P. aeruginosa with an equivalent efficacy.

The immunobiology of corneal HSV-1 infection and herpetic stromal keratitis

SUMMARYHuman alphaherpesvirus 1 (HSV-1) is a highly successful neurotropic pathogen that primarily infects the epithelial cells lining the orofacial mucosa. After primary lytic replication in the oral, ocular, and nasal mucosal epithelial cells, HSV-1 establishes life-long latency in neurons within the trigeminal ganglion. Patients with compromised immune systems experience frequent reactivation of HSV-1 from latency, leading to virus entry in the sensory neurons, followed by anterograde transport and lytic replication at the innervated mucosal epithelial surface. Although recurrent infection of the corneal mucosal surface is rare, it can result in a chronic immuno-inflammatory condition called herpetic stromal keratitis (HSK). HSK leads to gradual vision loss and can cause permanent blindness in severe untreated cases. Currently, there is no cure or successful vaccine to prevent latent or recurrent HSV-1 infections, posing a significant clinical challenge to managing HSK and preventing vision loss. The conventional clinical management of HSK primarily relies on anti-virals to suppress HSV-1 replication, anti-inflammatory drugs (such as corticosteroids) to provide symptomatic relief from pain and inflammation, and surgical interventions in more severe cases to replace damaged cornea. However, each clinical treatment strategy has limitations, such as local and systemic drug toxicities and the emergence of anti-viral-resistant HSV-1 strains. In this review, we summarize the factors and immune cells involved in HSK pathogenesis and highlight alternate therapeutic strategies for successful clinical management of HSK. We also discuss the therapeutic potential of immunoregulatory cytokines and immunometabolism modulators as promising HSK therapies against emerging anti-viral-resistant HSV-1 strains.