Comparative flow immunophenotypic features of the inflammatory infiltrates of Hodgkin lymphoma and lymphoid hyperplasia

Background: Hodgkin lymphoma (HL) is characterized by relatively few malignant Reed-Sternberg (RS) cells admixed within a reactive T cell rich inflammatory infiltrate. There is growing recognition that the HL-associated inflammatory milieu may enhance rather than inhibit growth of RS tumor cells. Since little is known of the immunophenotype of the HL inflammatory infiltrate we have performed a detailed retrospective comparison of the flow immunophenotype of HL and reactive lymphoid hyperplasia (RLH) to identify HL-specific immunophenotypic features. Methods: Single cell suspensions from 59 lymph nodes involved by HL (at initial diagnosis) and 38 lymph nodes involved by RLH were subjected to a battery of 3-color combinations of well-characterized fluorochrome-conjugated monoclonal antibodies (DAKO) to a number of lymphocyte subsets. Cells were analyzed on a FACSCalibur flow cytometer with CellQuest software (Becton Dickinson). Results: Overall, CD4+ T cells are increased and CD19+ B cells decreased in HL vs. RLH, yielding median T:B cell (CD3:CD20) ratios of 2.3:1 and 1.6:1, resp. There is no difference in median CD8+ T cell % (16% in HL & RLH). The T:B cell ratio is highest in nodular sclerosis (NSHL) and lymphocyte depletion (LDHL) subtypes, and lowest in mixed cellularity HL (MCHL). There is no significant difference in CD4:CD8 ratio in any comparison. NKT cells were slightly increased in HL vs. RLH, especially in MCHL. CD4+CD25+ regulatory T cells are significantly increased in HL (9%) vs. RLH (2%), especially in MCHL (29%) and NSHL (12%). EBV positivity in NSHL is associated with older age, decreased CD4+CD25+ regulatory T cells, CD4:CD8 ratio, and CD19/CD20+ B cells, and increased NKT cells, and CD14+ low forward-side scatter-gated monocytes. Conclusion: The cellular composition of the reactive lymphocytic infiltrate in HL differs significantly from that seen in RLH, with significant differences also noted between HL subtypes. In general, the HL infiltrate contains increased T cells (CD4+ and NKT subsets), decreased B cells, and increased regulatory T cells in comparison with RLH. The major difference between HL subtypes is decreased CD4+ T cells in MCHL as compared with NSHL and NLPHL. The most notable EBV-related difference in NSHL is increased regulatory T cells in EBV negative cases. While many differences in the reactive lymphocytic infiltrate of Hodgkin lymphoma and reactive lymphoid hyperplasia were identified, the sole difference that may prove to be of differential diagnostic value in flow cytometric analysis of HL versus RLH is the increased percentage of CD4+ bright CD25+ regulatory T cells in HL.