Cytokine patterns and pathogenicity in autoimmune diseases.

Cytokines are a large family of small proteins secreted by leukocytes and having an essential role in mediating the immune function. Many cytokines have multiple cellular sources and targets, as well as many natural inducers and inhibitors. These features and moreover the functional particularities of cytokines (autocrine and paracrine mode of action, overlapped activities, pleiotropic action, functioning as a complex regulatory network, and reciprocal down-regulation of the Th1 and Th2 cytokine groups) hampered the investigation of cytokines' role in autoimmune diseases (ADs). Despite this, the experimental and clinical studies have firmly documented the implication of cytokines in major pathophysiological and pathogenetic mechanisms associated with both the acute (onset and/or recurrence) and the chronic stages of ADs. The enhanced production of cytokines during the acute phase of systemic lupus erythematosus, rheumatoid arthritis and vasculitis has pathogenic effects such as appearance of anti-neutrophil cytoplasmic antibodies, initiation of vascular thrombosis and/or an increased production of autoantigens. The potent proinflammatory cytokines IL-1 and TNFalpha and also IL-8 and IFNalpha,gamma stimulate cells in different tissues to release harmful proteinases and reactive oxygen species, contributing to tissue damage. Some correlations have been found between serum cytokine levels and disease activity in certain systemic ADs. Studies investigating the cytokine pattern in ADs revealed the prevalence of the proinflammatory Th1-type cytokines in the target organ of patients with organ-specific ADs, such as multiple sclerosis and autoimmune thyroid disease, and heterogeneous cytokine profiles in patients with systemic ADs. A lot of factors, including the mechanism of tissue damage, the type of antigen-presenting cells and costimulatory molecules, and also the hormonal status, favor secretion of cytokines of Th1- or Th2-type in these patients. Beneficial effects have been obtained in patients with rheumatoid arthritis and Crohn disease by administering biotechnologically manufactured anti-TNFalpha antibodies or TNFalpha receptors. The risks of these cytokine-targeting therapeutical interventions are also discussed.