NF-κB transcription factor is a common event, which may occur through EBV infection (hence some cases positive for EBV) or other mechanism.  It is thought this process results in survival of germinal center B-cells, which would otherwise undergo apoptosis.  Hodgkin lymphoma cells typically represent a small number within the lesional tissue.  Hodgkin cells secrete varying cytokines that recruit other inflammatory cells, which make up the characteristic milieu (histiocytes, plasma cells, T-cell, and eosinophils).

 

Reed-Sternberg (HRS) cells are defined by two separate nuclear lobes with large nucleoli.  Mononuclear neoplastic cells are referred to as Hodgkin cells.  There is often a spectrum in appearance of the neoplastic cells with some HRS types but they may a minority.  Granulomatous inflammation may be present in biopsy specimens, and it important not to dismiss the granulomatous inflammation as the primary pathology (especially in small biopsy samples).

• Nodular Sclerosing CHL (65-70%), EBV-
• Lymphocyte-Rich CHL (~5%), ~40% EBV+
• Mixed-Cellularity CHL (20-25%), 70% EBV+
• Lymphocyte-Depleted CHL (<1%), >90% EBV+

Characteristic Immunohistochemical Features:

CD30	Positive in the malignant cells in almost all cases.  Membrane staining with Golgi area positivity.
CD15	Positive in the malignant cells in a majority of cases (75-85%).  The staining pattern is similar to CD30.  It should be noted that there is a lot a variability lab to lab in the performance of the antibody.
CD45	Usually negative
PAX_5	Dim expression in the lymphoma cells in >90% of the cases.  Helpful in differentiating cases from anapestic large cell lymphoma, which may be CD45 negative.
CD20	Usually negative, but may have dim variable subset expression in up to 20% of cases.
CD79a	Rarely positive in the lymphoma cells.
MUM1	Usually positive and usually intense.
EBV	Variable
EMA	Rarely positive and usually weak if positive.
OCT-2	Negative in 90% of cases.
BOB.1	Negative in 90% of cases.
ALK	Negative.

References