In the discovery of a new mechanism for the recognition between macrophages and tumor cells, the MHC class I component β2-microglobulin/LILRB1 protein, researchers used the gene modification of macrophages to knock out the gene for the LILRB1 protein and downregulated its expression on the membrane surface, allowing the macrophages to transform from the state of promoting the growth of tumor cells to eliminating the tumor cells (Figure 3C). Here, LILRB1 is linked to neoplasm.