KIR2DS4 and COVID-19: In line with these studies, higher frequencies of the functional A-telomeric activating receptor KIR2DS4 [35] and the inhibitory receptors KIR2DL1 and KIR2DL1/S1 [33] are associated with severe COVID-19, whereas a higher frequency of activating receptor KIR3DS1 in the presence of HLA-B*15:01 is associated with mild and/or moderate COVID-19 [35].