ITIH4 and HIV-1 infection: For example, during HIV-1 infection, the viral SU domain (gp120) binds to CD4 receptors expressed on the cells of the immune system, namely T lymphocytes (T-helper cells), cells of the monocyte lineage (microglia and macrophages), and dendritic cells, inducing a conformational change in both CD4 and gp120.