Effect of rhIL-2 on NK cells lacking CD56 and/or p75/AIRM1. Peripheral blood NK cells from a group 1 patient were labeled with CFSE, magnetically separated into CD56⁻ and CD56⁺ subsets, and then cultured in the presence of rhIL-2. (A) The 2 NK-cell subsets were analyzed by FACS at the indicated time intervals to assess their CD56 or p75/AIRM1 expression and their proliferation capability. The percentage of CD56⁺CD16⁺ NK cells detected in cultures containing purified CD56⁻ cells are indicated (bottom left). CFSE dilution of NK cells stained with anti-CD56 or anti-p75/AIRM1 is also shown (top and middle). Numbers in the middle panels refer to the percentage of p75/AIRM1⁺ NK cells. (B) CFSE dilution at different time intervals is comparatively shown for the purified CD56⁻ (gray profile) and CD56^dim (thick open profile) purified NK-cell fractions. In each histogram the CFSE staining of NK cells at day 0 is depicted (thin open profile). (C) After 7 days of culture in the presence of rhIL-2, cultures containing purified CD56⁻ or CD56⁺ NK cells were evaluated for CD107a expression after incubation with K562. The percentage of CD107a⁺ cells is shown for the CD56⁻ and CD56⁺ NK cells derived from cultures containing the purified CD56⁻ fraction (left) and for the CD56^bright and CD56^dim NK cells derived from the purified CD56⁺ fraction (right). (D) RT-PCR analysis of p75/AIRM1 transcripts was performed on total RNA extracted from the indicated NK-cell populations. In the p75/AIRM1 analysis the PCR products corresponding to the open reading frame (ORF) or to the alternative splicing forms (a.s.) are indicated. Molecular weights are labeled on the left. RT-PCR analysis of CD2 transcripts are shown as controls. On the right, the surface expression of p75/AIRM1 is shown on the analyzed NK-cell populations before (top histogram, unfractionated) and after FACS sorting (lower histograms, p75/AIRM1⁺ and p75/AIRM1⁻). The percentage of positive cells is indicated.