Given that host immune response is a key component during tumor growth and progression31, that high immune response has been correlated with better prognosis in melanomas27, and that our primary tumor data showed a remarkable increase in tumor expression of the anti-inflammatory cytokine IL-10 when host B1 receptor is absent (Fig. 2e), we investigated whether the content of immune cells in metastatic lungs of WT and B1−/− mice was altered. This evidence concerns the gene IL10 and neoplasm.