Fas ligand expression in Hodgkin lymphoma

Because previous investigations suggested involvement of the Fas ligand (FasL) in the selection process in the follicular dendritic cell (FDC)-associated cell cluster of the germinal center, we investigated the expression of FasL in Hodgkin lymphoma (HL) on protein and RNA level, while considering the Epstein-Barr virus status of the Hodgkin and Reed-Sternberg (HRS) cells. Tumor tissue from 47 patients with classic HL (32 nodular sclerosis [NS], 11 mixed cellularity [MC], and 4 lymphocyte-rich [LR]) was analyzed by immunohistochemistry for FasL, Fas, CD21, and CD23 and by Western blotting for FasL. FasL mRNA was detected by an exon 4-specific oligonucleotide and Epstein-Barr virus infection by in situ hybridization for Epstein-Barr virus early RNAs (EBER). Western blotting showed soluble and membrane-bound forms of FasL. Immunohistochemistry showed FasL expression in virtually all HRS of 94% of NS cases and 82% of MC cases. FasL expression did not correlate with the Epstein-Barr virus status of the HRS. Low FasL protein expression was found in some HRS of LR cases. FasL mRNA was detected in 39% of NS, 46% of MC, and 33% of LR cases. Seventy percent to 90% of the HRS cells expressed Fas. CD21 immunohistochemistry showed disrupted FDC networks in the tumor tissue with reduced and virtually absent expression of CD23 and FasL. These observations suggest that FasL expression in HRS cells and the absence of FasL in the FDC cluster represent a disturbed microenvironment that may be involved in the pathogenesis of HL.