Flagellin is the only known agonist of the toll-like receptor 5 (TLR5), and the flagellin—TLR5 interaction is implicated in the systemic inflammation and immune activation during HIV-1 infection, as flagellins can leak into blood circulation through the gut–blood barrier and activate TLR5 on the surface of epithelial cells and the immune cells, particularly in circulation monocytes and macrophages in gut tissues [6]. Here, TLR5 is linked to HIV-1 infection.