Cytokine expression and dendritic cell density in melanoma sentinel nodes

The sentinel lymph node (SLN) is the first draining node from the area in which a tumour is located. The presence or absence of SLN micrometastasis is an important prognostic factor for melanoma. As the first dissemination route for melanoma is lymphatic and we know that the immune system plays an important role in melanoma response, we hypothesize that melanoma and its corresponding SLN should constitute an immunological unit. Small portions of 54 SLNs from 37 patients undergoing selective lymphadenectomy were subjected to quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) to quantify messenger RNA (mRNA) transcripts of the following genes: tyrosinase, telomerase, cyclooxygenase-1 (COX-1), COX-2, granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-2 (IL-2), interferon-gamma (IFN-gamma), IL-4, IL-10 and IL-12. In addition, 11 non-sentinel lymph nodes (NSLNs) were excised from 11 of the 37 patients and the same study was performed. Immunohistochemistry with different antibodies against dendritic cells (DCs) was performed in 10 pairs of SLNs and NSLNs. Significantly higher mRNA expression of COX-2, GM-CSF, IFN-gamma and IL-10 was found in SLNs compared with NSLNs in the overall group. DCs, as labelled by S-100 and CD1a, were significantly decreased in NSLNs compared with SLNs. These data suggest that the initial increase in GM-CSF observed in SLNs could lead to the attraction of a high number of DCs to SLNs. However, the presence of certain immunosuppressive molecules, such as IL-10 and COX-2, could block their maturation and their ability to become efficient antigen presenters.