Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Review
. 2012 Apr;25(2):215-22.
doi: 10.1128/CMR.05028-11.

Epithelial cell responses to infection with human papillomavirus

Affiliations
Review

Epithelial cell responses to infection with human papillomavirus

Margaret A Stanley. Clin Microbiol Rev. 2012 Apr.

Abstract

Human papillomavirus (HPV) infection of the genital tract is common in young sexually active individuals, the majority of whom clear the infection without overt clinical disease. Most of those who do develop benign lesions eventually mount an effective cell-mediated immune (CMI) response, and the lesions regress. Regression of anogenital warts is accompanied histologically by a CD4(+) T cell-dominated Th1 response; animal models support this and provide evidence that the response is modulated by antigen-specific CD4(+) T cell-dependent mechanisms. Failure to develop an effective CMI response to clear or control infection results in persistent infection and, in the case of the oncogenic HPVs, an increased probability of progression to high-grade intraepithelial neoplasia and invasive carcinoma. Effective evasion of innate immune recognition seems to be the hallmark of HPV infections. The viral infectious cycle is exclusively intraepithelial: there is no viremia and no virus-induced cytolysis or cell death, and viral replication and release are not associated with inflammation. HPV globally downregulates the innate immune signaling pathways in the infected keratinocyte. Proinflammatory cytokines, particularly the type I interferons, are not released, and the signals for Langerhans cell (LC) activation and migration, together with recruitment of stromal dendritic cells and macrophages, are either not present or inadequate. This immune ignorance results in chronic infections that persist over weeks and months. Progression to high-grade intraepithelial neoplasia with concomitant upregulation of the E6 and E7 oncoproteins is associated with further deregulation of immunologically relevant molecules, particularly chemotactic chemokines and their receptors, on keratinocytes and endothelial cells of the underlying microvasculature, limiting or preventing the ingress of cytotoxic effectors into the lesions. Recent evidence suggests that HPV infection of basal keratinocytes requires epithelial wounding followed by the reepithelization of wound healing. The wound exudate that results provides a mechanistic explanation for the protection offered by serum neutralizing antibody generated by HPV L1 virus-like particle (VLP) vaccines.

PubMed Disclaimer

Figures

Fig 1
Fig 1
Cartoon illustrating the genomic organization of a typical mucosal high-risk HPV. The genome contains early and late regions, which relate to the positions of the genes within the genome and their timing of expression during the viral life cycle. The early region carries a number of genes which function at the level of viral replication and transcription, i.e., E2, E1, E6, and E7. E2 encodes a protein which has an auxiliary role in viral replication and also functions at the level of transcriptional regulation of the viral early genes. Many studies have shown that it is a negative regulator of viral gene expression. The E6 and E7 genes encode the major transforming proteins of the oncogenic HPVs, but it should be noted that although they are transforming proteins, they also have important roles in the normal viral life cycle. The late region encodes viral structural proteins, with L1 being the major capsid protein and L2 being the minor capsid protein. Control of early gene transcription and replication is conferred by the upstream regulatory region (URR), which contains promoter and enhancer elements as well as the viral origin of replication. Here the transcriptional apparatus assembles and generates polycistronic transcripts which utilize the early polyadenylation signal.
Fig 2
Fig 2
Papillomaviruses are absolutely species specific and tissue specific. HPV will infect and replicate in a fully differentiating squamous epithelium only. The virus infectious cycle is rather complex and can explain the duration of an HPV infection. It involves both temporal and spatial separation of viral protein expression. The virus first infects a keratinocyte in the basal layer of the epithelium as a consequence of microtrauma, i.e., an abrasion of the epithelium that exposes the basement membrane and basal cells. In the proliferative compartments of the epithelium, there is a phase of plasmid maintenance, the virus and cell replicate together, and the viral copy number is maintained at around 50 to 100 copies in the daughter cells. For the oncogenic viruses, in particular, viral gene expression is very tightly controlled during this phase. As long as the cell is dividing, the high-risk HPVs control the expression of their viral proteins very tightly. The E6 and E7 oncogenes are thus expressed at very low levels. When the host cell stops dividing and begins to differentiate into a mature keratinocyte, this provides a signal to the virus to activate all of its genes to increase the viral genome copy number to the thousands. In the case of incipient malignancy, control of E6 and E7 expression is lost, and gene expression in the cell becomes deregulated. In the top layers of the epithelium, all of the viral genes, including those encoding the L1 and L2 proteins, are expressed, and many thousands of viral genomes are encapsidated; these exit the cell as infectious virus particles. The time taken from infection to the generation of infectious virus is at least 3 weeks. HPV thus has a very long infectious cycle, has no blood-borne phase, and does not cause cell death.
Fig 3
Fig 3
HPV is efficient at evading recognition. The virus can globally downregulate keratinocyte innate immune sensors and suppress the type I interferon response, which is critical for the control of viral infection. There is no viremia and no virus-induced cell death; hence, there is no inflammation or danger signal to the immune system.
None

Similar articles

Cited by

References

    1. Akira S, Hemmi H. 2003. Recognition of pathogen-associated molecular patterns by TLR family. Immunol. Lett. 85:85–95 - PubMed
    1. Alazawi W, et al. 2002. Changes in cervical keratinocyte gene expression associated with integration of human papillomavirus 16. Cancer Res. 62:6959–6965 - PubMed
    1. Arany I, Goel A, Tyring SK. 1995. Interferon response depends on viral transcription in human papillomavirus-containing lesions. Anticancer Res. 15:2865–2869 - PubMed
    1. Arend WP, Palmer G, Gabay C. 2008. IL-1, IL-18, and IL-33 families of cytokines. Immunol. Rev. 223:20–38 - PubMed
    1. Bedoui S, et al. 2009. Cross-presentation of viral and self antigens by skin-derived CD103+ dendritic cells. Nat. Immunol. 10:488–495 - PubMed

MeSH terms

Substances