Downregulation of the major histocompatibility complex class I molecules by human herpesvirus type 8 and impaired natural killer cell activity in primary effusion lymphoma development

Primary effusion lymphomas (PELs) are invariably infected by human herpesvirus type 8 (HHV8) and often co-infected by Epstein-Barr virus (EBV). We found that expression of major histocompatibility complex class I (MHC-I) surface molecules was significantly decreased in PEL cells when compared with HHV8 negative lymphomas, irrespective of EBV infection. MHC-I downregulation rendered PEL cells sensitive to recognition and killing by natural killer (NK) cells. Intriguingly, analysis of MHC-I non-restricted cytotoxicity in two PEL patients indicated a reduced NK cell activity when compared with healthy individuals. These data suggest that PEL outgrowth may require an impaired NK cell function.