Abstract
In a previously performed population-based genetic screening analysis we found that polymorphisms in the HLA class I region are specifically associated with EBV-positive classical Hodgkin lymphoma(cHL)(
Diepstra et al., Lancet 2005;365:2216
). We now studied the expression of HLA class I and HLA class II in this population (n=450) by immunohistochemistry. HLA-B/C, HLA-G, beta-2-microglobulin and HLA-DP/DQ/DR staining was performed on formalin fixed paraffin embedded tissue sections, and HLA-DM and HLA-DO staining on frozen sections. Hodgkin-Reed Sternberg (HRS) cells showed cell surface expression of HLA class I in 37.5% (159/424) of cHL tumors and expression was observed predominantly in EBV-positive cases (73%; 103/141). Expression of HLA-G, a molecule known to enable evasion from natural killer cell responses, was found in 67% of the cases and was associated with absence of MHC class I and EBV. Only 58% of cHL cases showed HLA class II positive staining in more than 50% of the HRS cells (224/387). The non-classical HLA class II protein HLA-DM, essential for the loading of HLA class II with antigenic peptides was reduced or absent in HRS cells in 7 out of 10 HLA class II positive cases, whereas HLA-DO, the natural repressor of HLA-DM, was not or minimally expressed. Impaired expression of HLA-DM may prevent presentation of antigens at the level of individual HRS cells. Reanalysis of the genotyping data revealed an association of HLA class I positive cases with the known susceptibility polymorphisms in the HLA class I region. However, this association was stronger for the EBV-positive cases than for the HLA class I positive cases. Within the group of EBV-positive cHL patients, the same predisposing alleles were present in both HLA class I negative and positive cases, suggesting that the negative cases probably did express HLA class I during early pathogenesis. Finally, in cases with HLA class II expression on the HRS cells, a genetic association with the HLA class II region was found. These changes may influence (EBV) antigen presentation by HRS cells in cHL.Author notes
Corresponding author
2005, The American Society of Hematology
2005
