Cat COVID, CMV and Chemokines, Oh My!

Cytomegalovirus (CMV) is an important pathogen infecting most humans worldwide. CMV infection within immunocompromised individuals can cause severe morbidity and potential mortality. Disease during CMV infection is due to virus dissemination and subsequent inflammation. Host immune cells lie at the intersection potentially mediating both. The CMV-encoded viral chemokine vCXCL-1 is a proposed virulence factor in mouse models increasing immune cell recruitment and disease. However, the primary immune cell mediator is undetermined. To identify targets, Chapter 2 examines CXCR2 expression (receptor for vCXCL-1) among various mouse tissues and human peripheral blood under steady-state conditions. In vitro, isoforms of HCMV’s vCXCL-1 induce differential outcomes even when acting upon the same cells/receptors (termed functional selectivity), the in vivo consequences of which are unknown. In Chapter 3, recombinant MCMVs expressing vCXCL-1 in vivo, as well as purified chemokine in vitro, and protein modeling in silico help further characterize functional differences between viral and host chemokines. We additionally identified a conserved, unique region within the C-terminus of vCXCL-1. These observations provide the basis for future studies of CMV pathogenesis.

Following recruitment to a site of infection, viral uptake occurs infecting migrated cells. Prevention of viral entry is an attractive therapeutic target to lessen viral burden and disease. However, there are limitations in relating in vitro assays to in vivo, as MCMV derived in vivo displays altered entry phenotypes rendering attachment and entry inhibitors less effective. In Chapters 4 and 5 we further characterized differences between in vitro and in vivo derived MCMV. In Chapter 4, in vitro and in vivo virus display different dependencies on cell surface heparan sulfate proteoglycans (HS) for attachment, with in vivo virus less dependent on HS and potentially utilizing different moieties. Chapter 5 further demonstrates in vivo virus’ reduced HS interaction. In vivo virus was additionally found to be of a uniform size and contain submicron particle distributions (potentially extracellular vesicles) different from in vitro derived virus. While submicron particles did not appear to play a role to enhance infection in vitro, their exact role is unknown. These advances can hopefully better inform development of anti-CMV therapeutics.