Fas and Fas ligand are highly expressed in lymphocytes from cervical intraepithelial neoplasia and cervical cancer patients: A possible role for immune escaping

Abstract

Objectives: Infection with high-risk human papillomavirus is required to develop cervical cancer. Some viruses modulate the Fas/FasL signaling to evade the immune response; the role of these molecules in cervical cancer is not clear. In this study, we measured the expression levels of Fas and FasL mRNA, soluble proteins, and cell surface proteins in peripheral blood mononuclear cells from patients with low- and high-grade squamous intraepithelial lesions and cervical cancer in relation to healthy women, to gain new insights into the role of Fas/FasL in cervical cancer development.

Materials and methods: Fas/FasL mRNA expression was measured in cervical tissues and peripheral blood mononuclear cells from patients and healthy subjects; serum soluble proteins Fas/FasL were measured by ELISA, and cell-surface protein expression was detected by flow cytometry.

Results: Varying expression levels were found for both molecules. Cervical Fas and FasL mRNA expression was decreased in low- and high-grade lesions, but it was increased in cervical cancer cases. While, systemic Fas mRNA expression increased as malignity progressed; systemic FasL mRNA expression was increased in low- and high-grade lesions, but it was decreased in cancer patients. Soluble FasL levels decreased as lesions progressed, while soluble Fas levels increased. Finally, overexpression of Fas/FasL on the surface of peripheral blood mononuclear cells was found in patients with low-grade lesion with respect to healthy donors.

Conclusion: Fas and FasL act as negative modulators of the immune response, probably by removing specific cytotoxic T lymphocytes against papillomavirus -infected cells and tumor cells.

Keywords: Cervical intraepithelial – neoplasia; Fas ligand protein; Fas receptor; Gene expression; Uterine cervical neoplasms.

Figure 1

Fas and FasL mRNA local (cervix) and systemic expression in patients with differing lesion grades and cervical cancer. Medians ± Standard error (*: P<0.05). NCL: Non-cervical lesions. L-SIL: Low Squamous Intraepithelial Lesion. H-SIL: High Squamous Intraepithelial Lesion. CC: Cervical cancer

Figure 2.

Serum sFas and sFasL levels in patients with differing lesion grades and cervical cancer. Means ± Standard deviation (*: P<0.05). Non-cervical lesions. L-SIL: Low Squamous Intraepithelial Lesion. H-SIL: High Squamous Intraepithelial Lesion. CC: Cervical cancer; NCL: Non-cervical lesions

Figure 3

Fas and FasL expression in PBMCs from patients with Low Squamous Intraepithelial Lesion (L-SIL) analyzed by flow cytometry. Means ± Standard deviation (*: P<0.05). L-SIL patients (black bars), healthy women (grey bars)

Figure 4

Schematic representation of the role of Fas and FasL in CC progression. The main event in human papillomavirus (HPV)-induced carcinogenesis is the infection of cervical epithelial cells at the basement membrane. Upon infection, an average of 2–3 years are required to develop L-SIL and H-SIL. The immune system plays a key role in HPV-induced carcinogenesis, since more than 90% of high-risk HPV infections regress, as well as most of the low-grade lesions (75%). The long period of time between the viral infection and the development of an invasive disease implies a failed immune response, crucial for cancer progression. A) Upon HPV infection, Fas and FasL are overexpressed at the systemic level, on the surface of immune cells, and in the serum of L-SIL patients, possibly derived from activated lymphocytes in response to HR-HPV infection. B) FasL levels are increased in cervical cancer cells in correspondence with the lesion grade, with the highest concentrations measured in cancer patients. This may lead to release of FasL from cervical cancer cells, which interacts with the Fas receptor on the surface of T lymphocytes, probably inducing apoptosis. C) These events are key for the impairment of immune responses allowing the persistence of HPV and eventually results in cell transformation