Interferon-γ and Tumor Necrosis Factor-α Sustain Secretion of Specific CXC Chemokines in Human Thyrocytes: A First Step Toward a Differentiation between Autoimmune and Tumor-Related Inflammation?

Context:Chemokines are chemotactic cytokines responsible for the attraction and recruitment of different cell types during leukocyte infiltration, the histopathological hallmark of autoimmunity. Previous data demonstrate that thyrocytes secrete CXC chemokines, particularly CXCL8 and CXCL10. However, the physiopathological significance of such secretion and the effects of a combination of proinflammatory stimuli in terms of preferential CXCL8 and CXCL10 release remain unclear.Objective:The aim of this study was to investigate whether the secretion of chemokines by human thyrocytes is a generalized inflammatory response or whether it is dependent upon specific proinflammatory stimuli.Methods:CXCL8 and CXCL10 were measured in supernatants of human thyrocytes in primary cultures basally and after 24 h stimulation with interferon-γ (IFNγ) (1000 U/ml) and TNFα (10 ng/ml), alone or in combination.Results:CXCL8 but not CXCL10 was detected in basal conditions. The two chemokines showed differences in their response to proinflammatory cytokines. Indeed, significant secretion of CXCL10 was induced by IFNγ (P < 0.01) and not TNFα, whereas CXCL8 was secreted in response to TNFα (P < 0.01) being inhibited by IFNγ (P < 0.01). The combination of TNFα plus IFNγ synergistically increased the IFNγ-induced CXCL10 secretion (P < 0.01) and reversed the TNFα-induced CXCL8 secretion (P < 0.01).Conclusions:These results confirm that human thyrocytes secrete CXC chemokines and demonstrate that the secretion of CXCL8 and CXCL10 is sustained by specific proinflammatory cytokines or their combination, which ultimately determines the nature of the infiltrating lymphocytes in human thyroid diseases. These results indirectly support a major role for CXCL10 in thyroid autoimmunity whereas CXCL8 might be involved in tumor-related inflammation