Localization of IL-10 mRNA in different cells in sentinel and non-sentinel nodes of melanoma patients by the RT in situ PCR technique Free

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It has been proposed that sentinel lymph nodes (SLNs) are exposed to and modulated by bioactive molecules generated by tumor cells and tumor-associated cells. IL-10 is a major immune regulator that immunosuppresses SLNs and may render them susceptible to metastases (Cochran, et al. Nature Rev Immunol, 2006, 6: 659-670). We have shown that anti-inflammatory IL-10 is expressed by invasive primary melanoma cells and metastatic melanoma cells (Itakura, et al. Modern Pathol, 2004, 17: 94A). IL-10 produced by metastatic tumor cells in LN appears to play a role in local and regional immunosuppression, though tumor-free nodes may also be immunosuppressed. Primary melanoma-associated macrophages also express IL-10 and such cells, as well as free IL-10 molecules, can pass via the lymphatics to affect SLNs. IL-10 mRNA has been detected in tumor-positive and tumor-negative SLNs and non-sentinel nodes (NSLNs). To investigate the localization of IL-10 mRNA expressed by cells other than tumor cells, we applied the RT in situ PCR technique to tumor-free sections from 19 SLNs and 15 NSLNs from melanoma patients. IL-10 mRNA was detected in 19/19 (100%) SLNs and 11/15 (73%) NSLNs. Histology revealed that IL-10 mRNA was mainly expressed by macrophages in the cortical and marginal lymphatic sinuses. In 50% of SLNs and NSLNs, diffuse or clustered lymphocytes in the paracortical areas also expressed IL-10 mRNA. These results indicate that IL-10 positive macrophages can be detected in SLNs and NSLNs. These cells are a source of bioactive molecules that can induce down-regulation of immune functions including dendritic cell activity in the paracortical area in the absence of metastatic melanoma.