Cytomegalovirus (CMV) infects a remarkably wide range of human cells, which is a big part of what makes it so successful at establishing lifelong infection. The four cell types most frequently infected in people with active CMV disease are endothelial cells (blood vessel linings), epithelial cells (skin and organ linings), fibroblasts (connective tissue cells), and smooth muscle cells. But the full list extends well beyond those four, touching nearly every organ system in the body.
The Main Cellular Targets
CMV is not picky. Unlike viruses that home in on one or two cell types, CMV has evolved separate molecular toolkits for breaking into different kinds of cells. The virus carries two distinct protein complexes on its surface: a three-part complex (called the trimer) and a five-part complex (called the pentamer). The trimer is sufficient for infecting fibroblasts, the structural cells found in skin, tendons, and connective tissue throughout the body. The pentamer is required for infecting epithelial cells and endothelial cells, which line organs, glands, and blood vessels.
These aren’t just lab observations. Autopsy studies of immunosuppressed patients with widespread CMV infection consistently show viral proteins inside endothelial cells, epithelial cells, fibroblasts, smooth muscle cells, and certain white blood cells. Epithelial cells, after endothelial cells and white blood cells, are the cell type most commonly infected in patients with disseminated disease.
How CMV Gets Into Different Cells
The virus uses different doors depending on the cell type. To enter fibroblasts, the trimer complex latches onto a receptor called PDGFR-alpha on the cell surface. To enter epithelial cells, it relies on a receptor called OR14I1, a multipass membrane protein that the pentamer complex binds to. This receptor is required for the virus to attach, enter, and infect epithelial cells. Once bound, it triggers a signaling cascade inside the cell that allows the virus to be pulled in through a process called endocytosis.
This dual-entry system explains why CMV can reach so many tissues. Fibroblasts are everywhere in the body, so the trimer gives CMV broad access to connective tissue. The pentamer opens the door to the epithelial and endothelial cells that line organs, glands, and blood vessels. Together, these two pathways let CMV reach virtually any part of the body.
Immune Cells as Transport Vehicles
One of CMV’s most effective strategies is hijacking immune cells to travel through the body. Macrophages, the large immune cells that patrol tissues and engulf invaders, are among the first cells CMV encounters. They are the most abundant immune cell at mucosal surfaces in the respiratory and gastrointestinal tracts, which are common entry points for the virus.
Monocytes, the circulating precursors to macrophages, are key to CMV’s spread. A specific subset of monocytes called patrolling monocytes crawl along the inner lining of blood vessels, where they can pick up CMV from infected endothelial cells. These infected monocytes then carry the virus to distant organs like the spleen, salivary glands, and lungs. When monocytes arrive at a new tissue and mature into macrophages, viral replication can restart, seeding infection in a new location. Infected monocytes can also pass CMV back to endothelial cells, creating a cycle of infection between blood vessel walls and circulating immune cells.
Where CMV Hides for Life
After the initial infection clears, CMV doesn’t leave the body. It enters a dormant state called latency in specific cell types, primarily CD34+ hematopoietic progenitor cells. These are the stem cells in bone marrow that give rise to all blood cell types. Among the subpopulations of these progenitor cells, common myeloid progenitors make up the largest share (about 27%), followed by hematopoietic stem cells (about 21%) and granulocyte-monocyte progenitors (about 14%).
CD14+ monocytes can also harbor latent CMV without producing new virus. The virus essentially sits quietly inside these cells, carrying a small set of latency-specific genes that help it avoid immune detection. When the immune system weakens, whether from immunosuppressive drugs, HIV, or other causes, the virus can reactivate as these progenitor cells differentiate into mature immune cells. This is why CMV reactivation is such a serious concern after organ transplantation or during advanced HIV disease.
Blood Vessel Cells and Heart Disease
CMV’s ability to infect endothelial cells has implications beyond acute illness. CMV infection of blood vessel linings triggers an inflammatory response: infected endothelial cells ramp up production of inflammatory signaling molecules, display more adhesion molecules that attract white blood cells, and become more permeable. The virus also stimulates new blood vessel growth (angiogenesis) by activating growth factor receptors and integrins on endothelial cell surfaces.
CMV-positive individuals have a significantly increased risk of coronary artery disease. In transplant recipients, CMV seropositivity correlates with more severe atherosclerosis in transplanted hearts and higher rates of graft rejection. Animal studies confirm this: rodent CMV infection worsens atherosclerotic lesions and accelerates the vascular scarring that leads to transplant rejection. The proposed mechanism is that CMV infection of endothelial cells kicks off an inflammatory cascade, recruiting immune cells and promoting the formation of new, fragile blood vessels within arterial plaques.
Epithelial Cells and Viral Shedding
Epithelial cells in specific organs play a critical role in how CMV spreads between people. Kidney epithelial cells and mammary (breast) epithelial cells are both permissive to CMV infection, expressing viral proteins within 72 hours of being infected. These cells sequester the virus and release it gradually, which is why urine and breast milk are the two main routes of CMV transmission, particularly from young children and breastfeeding mothers.
Salivary gland epithelial cells are another major shedding site. The prolonged, slow release of virus from these epithelial tissues means that a person can shed CMV in saliva, urine, and breast milk for months or even years, often without symptoms.
Cells of the Developing Brain
Congenital CMV infection, when the virus crosses the placenta and reaches a developing fetus, is the leading infectious cause of intellectual disability and hearing loss in the developed world. The virus targets neural progenitor cells, the stem cells that build the fetal brain. By infecting these cells, CMV can disrupt normal brain development at its most fundamental level, interfering with cell differentiation and the formation of brain structures.
Only 10 to 15% of babies with congenital CMV show signs at birth. But among those with symptomatic infection, 60 to 90% develop long-term neurological problems including intellectual disability, motor impairment, hearing loss, and vision abnormalities. Even among babies who appear healthy at birth, 10 to 15% will eventually develop neurological complications.
Retinal Cells and Vision Loss
In the eye, CMV targets retinal pigment epithelial (RPE) cells, the layer of cells that supports the light-sensing retina. CMV retinitis was one of the most feared complications of AIDS before effective HIV treatment became available, and it remains a threat for severely immunosuppressed individuals. RPE cells show a distinctive pattern of CMV infection: the virus replicates slowly in these cells compared to fibroblasts, with a low frequency of early viral protein expression. This slower replication may actually help the virus persist in the retina without triggering an immediate immune response, setting the stage for progressive tissue destruction.
How CMV Spreads Between Cells
CMV doesn’t rely solely on releasing free-floating viral particles to infect new cells. It also spreads through direct cell-to-cell contact, passing from one infected cell to its neighbor. This matters because cell-to-cell spread is largely resistant to antibodies. In epithelial cells, cell-to-cell transmission is the dominant mode of spread for all viral strains, which helps explain why antibody-based immune responses struggle to fully control CMV in mucosal tissues. In fibroblasts, different viral strains vary: some spread mainly through free virus particles and are highly sensitive to neutralizing antibodies (which reduced their spread by 55 to 70%), while others relied on direct cell-to-cell transfer and were barely affected by the same antibodies (only a 25% reduction). This dual spreading strategy helps CMV persist even in people with strong antibody responses.