Expression of HPV L1 capsid protein in cervical specimens with HPV infection

We tried to investigate the expression rate of human papillomavirus (HPV) L1 capsid protein in uterine cervical specimens and correlate it with the grade of dysplasia, HPV genotype and age of the patients. Among uterine cervical specimens proved to have HPV by DNA genotyping test, eighty cytology-biopsy matched cases and 22 unmatched cytology specimens were selected. Immunostaining for L1 capsid protein was performed on both cervical smears and tissue sections. The L1 capsid protein was expressed mainly in the nuclei, but occasionally in the cytoplasm of cells located in the superficial layer of squamous epithelium. The immunostaining for L1 capsid protein showed positive reaction in 47 cases (46.1%) of cervical smears and in 10 cases (12.5%) of tissue sections (P = 0.001). Cytologic diagnosis revealed a higher expression rate in LSILs (25/33; 75.8%) than in HSILs and cervical cancers (8/20; 40.0% and 2/5; 40%, respectively) (P = 0.006). In LSILs, cases with low-risk type HPV showed a higher L1 capsid expression rate than those with the high-risk type HPV (88.9% vs. 70.8%). The L1 capsid expression rate decreased in the over-40-year-old age group compared to the younger age (49.2% vs. 50.8%). Cytology smears were superior to tissue sections for the detection of L1 capsid protein expression. LSILs and HPV low-risk group showed higher L1 capsid expression rate than HSILs and HPV high-risk group, which suggests that L1 capsid expression might be related to a favorable disease biology.