FIG 4.

Siglec-9 marks activated and mature CD56^dim NK subpopulation in vivo. (A) Comparisons of the expression of CD16 (FcγRIII; mediator of ADCC), CD57 (maturation marker), NKG2C (activating receptor), and NKG2A (inhibitory receptor) on Siglec-9⁺ and Siglec-9^– CD56^dim NK cells obtained from 79 individuals with three COVID-19 disease states (negative; n = 12, mild; n = 26, and hospitalized; n = 41). Siglec-9⁺ cells exhibit higher levels of CD16, CD57, NKG2C, and lower levels of NKG2A compared to Siglec-9^– cells. Wilcoxon’s signed-rank tests were used to compare the Siglec-9⁺ and Siglec-9^– CD56^dim NK cells within each COVID-19 disease state group. Mann-Whitney U tests were used to compare disease state groups. (B) Comparisons of CD16, CD57, NKG2C, and NKG2A expression on Siglec-7⁺ and Siglec-7^– CD56^dim NK cells. Siglec-7⁺ cells exhibited higher levels of CD16, NKG2C, and NKG2A than Siglec-7^– cells. No differences were observed in CD57 expression between the Siglec-7⁺ and Siglec-7^– cells. As in panel A, Wilcoxon’s signed-rank tests were used to compare the Siglec-7⁺ and Siglec-7^– CD56^dim NK cells within each COVID-19 status group, and Mann-Whitney U tests were used to compare the status groups.