Wild-Type Human Adenovirus (Serotype 37)

Epidemic keratoconjunctivitis (EKC) is a serious infectious eye disease that affects 20 to 40 million people worldwide each year. EKC is mainly caused by six human adenoviruses (HAdVs): HAdV-8, -19, -37, -53, -54, and -56. Among them, HAdV-8, -19, and -37 use sialic acid-containing glycans as cellular receptors. αVβ3, αVβ5, and some other integrins facilitate the entry of other HAdVs into cells and their release into endosomes. Here, researchers investigated global integrin expression on human corneal cells and found that α2, α3, α6, αV, β1, and β4 subunits were expressed in human corneal epithelial in situ and/or human corneal epithelial (HCE) cell lines, but no or little expression of α4, α5, β3, or β5. The integrins used by HAdV-37 were also identified through a series of binding and infection competition experiments and different biochemical approaches. Taken together, these data indicate that HAdV-37 uses αVβ1 and α3β1 integrins to infect human corneal epithelial cells. Furthermore, to confirm the relevance of these integrins to the HAdV-37 life cycle, the researchers developed a corneal multilayer tissue system and found that HAdV-37 infection was closely associated with the expression patterns of αV, α3, and β1 integrins.

To further explore the interaction between HAdV-37 and integrins at the cellular level, the researchers quantitatively analyzed the co-staining of AF555-labeled HAdV-37 virions with integrins αV and α3 at different time points after infection. To comprehensively study the virus invasion process, virions were incubated with cells on ice for 30 minutes (T = 0) or at 37°C for 15 or 30 minutes (T = 15 or T = 30), unbound virions were washed away, and the colocalization of virions with integrins was analyzed. At these time points, approximately 20% to 40% of the labeled virions colocalized with the α3 or αV subunits on HCE cells (Figure 1A and B). To verify colocalization, the researchers performed a pixel shift analysis, in which the pixels in the red HAdV-37-AF555 staining were shifted by 1 μm in the x and y directions and 0.5 μm in the z direction before analysis. The colocalization percentages between shifted HAdV-37 and original HAdV-37 and integrins were compared using paired t-tests (P = 0.05). Results showed statistically significant differences between true colocalization and random colocalization for αV (P = 0.0119) and α3 (P = 0.0447) and HAdV-37 in the 30-minute samples.

Figure 1. HAdV-37 virions colocalize with α3 and αV integrins on HCE cells. (Storm R J, et al., 2017)