Human CAP–37, a Cationic Protein, Demonstrates Direct Antiviral Activity against Adenovirus Types 3 and 5 and Herpes Simplex Virus in vitro

Abstract

Abstract: : Purpose: CAP–37, an inflammatory mediator, is an effector molecule of innate immunity expressed in PMNs, platelets and corneal epithelium with potent chemotactic, antibacterial and antifungal activity. CAP–37 is a part of the ocular host defense and expression in the corneal epithelium is significantly upregulated following S. aureus infection in the rabbit keratitis model (Ruan 2002). The goal of the current study was to determine whether the antimicrobial activity of CAP–37 also encompasses pathogenic viruses. Specifically, we tested CAP–37 for antiviral activity against the two most common viral ocular surface pathogens: adenovirus (Ad) (a non–enveloped virus) and herpes simplex type 1 (HSV–1) (an enveloped virus) in a direct inhibition time kill assay. Methods: Approximately 5 x 10⁴ pfu of clinical isolates of Ad3, Ad5, Ad8, Ad19, and HSV–1 McKrae were separately incubated for 4 hours at 37^oC with 500 µg/ml of CAP–37 (native), three CAP–37 substituted peptides (serine for cysteine at position 26, 42 and both) or PBS. After incubation, the samples were immediately diluted 1:10 in cold tissue culture media containing 10% FBS to inactivate the peptides. Titers were determined on A549 cells. Each experiment was repeated 6–7 times to enable statistical evaluation. Results: Compared to PBS, direct incubation with CAP–37 (native) resulted in a significant reduction (P < 0.05) in viral titers at 4 hours for Ad3 (1.2 logs), Ad5 (2.2 logs) and HSV–1 McKrae (1.6 logs). There was no significant antiviral effect for CAP 37 against Ad8 or Ad19. Compared to CAP–37 (native), the three substituted CAP–37 peptides generally demonstrated less (Ad 3, Ad 5) or no viral inhibition (Ad 8, Ad 19). In contrast, both native and substituted CAP–37 peptides demonstrated comparable inhibition of HSV–1 McKrae. Conclusions: CAP–37 demonstrated significant antiviral activity in vitro against Ad 3, Ad5 and HSV–1. This preliminary data suggests that the antimicrobial activity CAP–37 may be a part of the ocular innate immune response that also protects against some viral pathogens. The apparent failure of CAP–37 to inhibit oculotropic Ad serotypes 8 and 19 may be a part of successful immune evasion strategy that requires further elucidation.

Keywords: adenovirus • herpes simplex virus • immunomodulation/immunoregulation