Immunochemical analysis of HPV L1 capsid protein and p16 protein in liquid-based cytology samples from uterine cervical lesions.

HPV L1 capsid protein is expressed together with the production of infectious viral particles, but its expression and relation to p16 expression, which has been a surrogate marker for human papilloma virus (HPV) infection in cervix, are little studied in cytology samples. The authors aimed to elucidate the relation between L1 capsid protein and p16 protein expressions in liquid-based samples from uterine cervical lesions. Immunochemical analyses using antibodies against L1 capsid protein and p16 protein were carried out on cytological materials obtained from uterine cervical lesions of low-grade squamous intraepithelial lesions (LSILs), high-grade squamous intraepithelial lesions (HSILs), and squamous cell carcinomas (SCCs). L1 capsid protein was positive in 30% of LSILs and 12% of HSILs, but in 0% of SCCs. In contrast, p16 protein was positive in 55% of LSILs, 100% of HSILs, and 100% of SCCs. L1-positive cells were only observed in the superficial layer, whereas p16-positive cells were seen throughout the full thickness of the epithelium. The relation between L1 capsid protein and p16 protein, p16(-)/L1(+) cases represented 44% of LSILs, but 0% of HSILs, and 0% of SCCs, whereas p16(+)/L1(-) cases represented 82% of LSILs, 88% of HSILs, and 100% of SCCs. Expression of L1 capsid protein decreased with lesion progression from LSILs to HSILs and SCCs, whereas p16 protein was positive in all HSILs and SCCs. The correlation between L1 and p16 expressions suggests that L1(-)/p16(+) cases have the potential for progression, whereas L1(+)/p16(-) and L1(-)/p16(-) cases may be nonprogressive lesions or potentially in remission.