B-and T-Lymphocyte distribution in benign and malignant lymphoepithelial lesions of the parotid gland: correlation with epstein-Barr virus expression and a proposed mechanism of malignant transformation

ABSTRACT

Epstein-Barr virus expression in malignant lympoepithelial lesions [LEL] of the parotid gland has been well established. The virus is occasionally expressed in benign, IEL, especially in immunocomprmised hosts. The pathogenesis of the disease as it related to virus expression and lymphocyte subsets has not been clearly defined. In this study, we attempted to identify B- and T-lymphocyte distribution in the lesions as it related to EBV expression in LEL[s] of the parotid gland. Formalin-fixed paraffin-embedded sections of 18 cases of LEL of the period gland were immunohistochemically tested for the distribution of B- and T-lymphocytes in the lesions, using the antibodies L-26 [CD 20] for B-lymphocytes and UCHL-1 [CD-45RO] for T-lymphocytes. The sections were also tested by in situ hybridization for EBV mRNA expression, using the EBER-1 probe specific for EBV-1 gene. The 18 lesions included seven malignant LEL, seven benign LEL and four benign lymphoepithelial cysts. All malignant LEL[s] showed a high and diffuse level of epithelial expression of EBV Mran. Of the 11 benign lesions, only one cases showed focal epithelial expression of EBV mRNA. This was a case of benign LEL in an HIV-positive male. All the benign lesions, except that expressing EBV mRNA, showed a T-/B-lympocyte ratio averaging 21. All cases expressing EBV mRNA, including the case of benign LEL in the HIV-positive patient, showed a T-/B-lymphocyte ratio averaging 13. Our findings suggest that a T-lymphocyte-mediated immune response may play an essential role in suppressing proliferation of EBV in benign LEL of the parotid gland. This immune mechanism may be significantly disturbed in the malignant lesions, leading to uncontrolled viral replication and carcinogenesis