The Human Papillomavirus, commonly known as HPV, encompasses a widespread group of viruses. These prevalent viruses primarily target epithelial cells, which form the protective linings of various body surfaces. Such cells are found in areas like the skin, the cervix, and the lining of the throat. Understanding how HPV interacts with these cells is important for comprehending its implications for health.
How HPV Alters Human Cells
The term “HPV cells” refers to human cells that have become infected by the Human Papillomavirus. When HPV infects an epithelial cell, it inserts its genetic material, its DNA, into the host cell. The virus then hijacks the cell’s internal machinery to produce more viral components, essentially turning the host cell into a virus-making factory.
High-risk types of HPV, which are those associated with cancer, produce two proteins called E6 and E7. These viral proteins interfere with the host cell’s natural regulatory systems. E6 targets and degrades the tumor suppressor protein p53, while E7 inactivates pRb. These proteins normally act as “brakes” on cell growth, preventing uncontrolled division.
By disabling p53 and pRb, the E6 and E7 proteins allow the infected cell to bypass its normal checkpoints and grow and divide without proper regulation. This uncontrolled proliferation is a hallmark of HPV infection at the cellular level. A specific type of abnormal epithelial cell, called a koilocyte, is a classic microscopic sign of HPV infection, characterized by a large, irregular nucleus and a clear halo around it.
Identifying Abnormal Cell Changes
Detecting abnormal cell changes caused by HPV involves screening tests. The Pap test is a widely used method which collects cervical cells for microscopic examination. Pathologists look for changes in cell size, shape, and organization, including the presence of koilocytes, indicating HPV infection.
An HPV test is another diagnostic tool, which identifies high-risk HPV DNA in cell samples. It determines if a high-risk HPV infection is present, useful when combined with a Pap test. Screening results help classify the degree of cellular abnormality.
Common classifications include LSIL (low-grade squamous intraepithelial lesion), indicating minor cell changes often associated with temporary HPV infections. HSIL (high-grade squamous intraepithelial lesion) signifies more significant, potentially precancerous changes in cervical cells. These classifications guide further monitoring and treatment decisions.
The Progression from Infection to Cancer
Most HPV infections are temporary and do not cause long-term health problems. The body’s immune system clears the virus within one to two years. However, a small percentage of high-risk HPV infections can persist for many years.
Persistent high-risk HPV infections can lead to an accumulation of genetic errors in infected cells. As the viral proteins E6 and E7 continue to disrupt cellular regulation, cells may undergo further genetic alterations. This sustained disruption can gradually push cells towards a precancerous state.
Cervical Intraepithelial Neoplasia (CIN) describes these precancerous changes, categorized from CIN 1 to CIN 3. CIN 1 represents mild changes, while CIN 2 and CIN 3 indicate more severe changes. Progression from initial HPV infection to invasive cancer is a slow process, often taking 10 to 20 years, and is not an inevitable outcome.
The Body’s Response and Medical Interventions
The immune system effectively clears most HPV infections. Over 90% of individuals clear the virus within two years. When the immune system clears the virus, abnormal cells often revert to their normal state without specific treatment.
For persistent infections leading to high-grade precancerous changes (HSIL or CIN 2/3), medical interventions are available. These procedures remove or destroy affected tissue to prevent progression to invasive cancer. Common treatments include Loop Electrosurgical Excision Procedure (LEEP) or cryotherapy.
LEEP involves using a thin, electrically heated wire loop to remove the abnormal tissue from the cervix. Cryotherapy, conversely, uses extreme cold to freeze and destroy the abnormal cells. These targeted treatments effectively manage precancerous lesions, ensuring that the identified abnormal cells are addressed before they can develop into cancer.