Detection of human papillomavirus capsid antigens in various squamous epithelial lesions using antibodies directed against the L1 and L2 open reading frames

HPV6 and HPV16 infect the squamous epithelium of the genital tract and are thought to be involved in the pathogenesis of benign and malignant lesions. HPV6 is primarily found in benign condylomas whereas HPV16 is present in dysplasias and in invasive squamous cell carcinomas. To examine the expression of the major and minor capsid proteins in these lesions polyclonal antisera directed against bacterially derived fusion proteins harboring different restriction fragments of the L1 and L2 ORFs of HPV6b and HPV16 were generated. L1 ORF-specific antisera were not type-specific and detected the major capsid antigen in lesions infected with related HPV types. Anti-L2 ORF antisera could distinguish among HPV1, HPV6, and HPV16 when the fusion protein used as the immunogen did not harbor the amino-terminus of the L2 ORF. The anti-L1 ORF antisera were employed to detect the major capsid protein in various lesions by immunohistochemical staining. Lesions harboring HPV16 were positive in a high percentage of cervical intraepithelial neoplasia I–II (87%), and less frequently in carcinomas in situ (29%) or invasive carcinomas (17%). In all cases capsid antigen expression was restricted to cells showing some differentiation at the surface or periphery of the lesion.