Metastatic melanoma cells interact with the reticular fibres of the lymph node

Murine B16 melanoma sublines showing enhanced metastasis to lymph nodes were selected in vivo. Successive selections of tumours metastasizing from the footpad to para-aortic nodes yielded variant tumour cell lines, including an amelanotic line, with moderately increased potential for lymph node metastasis. The phenotype of the variant cells was distinct from that of the parental cells. The lymph node-selected cells had extensive dendritic-like pseudopodial projections and were more motile than the parental cells. In addition, the variant cells were more efficient than the parental cells in attaching to and spreading on preparations of lymph node extracellular matrix. This matrix is composed of an array of reticular fibres containing a core of collagen type III decorated with a basement membrane-like material rich in laminin and type IV collagen. In adhesion assays, the melanoma cells attached best to laminin, collagen, and fibronectin, and poorly to the interstitial matrix proteins collagen types I and III. This pattern of ligand preference was confirmed in adhesion assays to cryostat tissue sections of amnion, in which the tumour cells attached to the basement membrane aspect but not the interstitial stromal matrix. Experiments using specific antibodies established that cell attachment to lymph node reticular fibres was mediated by the beta 1 class of integrin receptor complexes. These results indicate that highly motile variant B16 sublines can be selected for distant lymphatic dissemination, and that interaction between invasive tumour cells and nodal reticular fibres may facilitate this metastatic process.