Hodgkin's disease is characterized by an immune response in the involved tissues that is predominantly CD4 mediated. The CD4+ T-cells are CD45RO+ and CD45RBdim, they express several activation markers but lack CD26, and in vitro can be stimulated to produce gamma-interferon and IL-4, but not IL-2. This is not the usual immunophenotype and cytokine production pattern of Th1, Th2 or Th0 cells and may be a reflection of anergy. The cause of such an anergic reaction is not clear since RS cells express HLA class II as well as the co-stimulator molecules CD80 and CD86. It is possible that a (hypothetical) super antigen expressed on the RS cells may play a role. The absence of IL-2 production however explains the absence of a CD8 mediated response. In addition to that, RS cells generally do not express HLA class I, which allows them to escape CD8 mediated responses. The link between the ineffective immune response in the tissue and the generalized immune deficiency in Hodgkin's disease may consist of several components. These include the influx of mature T-cells into the affected tissues, the secretion of inhibitory molecules by the neoplastic cells and the spill-over of the anergic T-cell response into the general circulation by either the Hodgkin related antigen or also as a result of an IL-4 dominated response. The latter possibility may also be related to the hyper-gamma-globulinaemia and the frequently observed high IgE levels.