Cytokines are a heterogeneous group of regulatory proteins often sharing biological activites. Attention has been drawn to their role in inflammatory and hemorrhagic processes, as well as in the immune response. Cytokines are produced by various cell types (lymphocytes, monocytes-macrophages and others non-leucocytic cells). The major cytokines secreted by manocyte/macrophage (m-MØs) include tumor necrosis factor (TNF)α, which causes tissue necrosis and prompts death by apoptosis, and interleukin (IL)-1, which displays chemotactic activity, and is also involved in the induction of apoptosis during different viral diseases. These two cytokines trigger production of the major pyrogenic cytokine IL-6, which is involved both in hepatocyte production of acute-phase proteins and in the regulation and differentiation of several cell types. These cytokines appear to be associated with increased vascular permeability, and reports suggest that they are in part responsible for the hemorrhaging characteristic of several human and animal viral diseases. Attention is also drawn to the procoagulant activity of both TNFα and IL-1 and to a lesser extent of IL-6, as well as to the involvement of TNFα, together with tissue damage, in activation of the extrinsic coagulation pathway and in the platelet aggregation as cause of thrombocytopenia.

The functions of IL-12 include participation in inflammatory processes and stimulation of specific cytotoxicity of T cells and natural killer (NK) cells, supporting T helper (Th)Cells differentiation, specially Th1, and inducing IL-2 production by these cells.