CD4 and cutaneous melanoma: To overcome the limitations of light microscopy, we performed 7-color multiplex immunohistochemistry on whole tissue sections from 103 human cutaneous melanoma samples with antibodies against TLS-defining molecular and cellular components: CXCL13, a key chemoattractant orchestrating the cellular composition of TLS, CD20 and CD4 for detection of B cells and T(helper) cells, CD21 and CD23 for the presence of a network of immature and mature follicular dendritic cells (FDCs), respectively, and BCL6, a key transcriptional regulator in B cells and T cells for germinal center formation.