Based on our observation of increased levels of Gal-9 in natural HIV-1 infection, we sought to next investigate whether Gal-9 could modulate NK cell function in vitro. To address this question, we compared NK cell function following treatment with soluble Gal-9 to that upon exposure to major histocompatibility complex (MHC)-deficient target cells (i.e. K562 cells). Here, LGALS9 is linked to HIV-1 infection.