Natural killer (NK) cells selected by IL-2-induced rapid adherence to plastic and called A-NK cells represent a phenotypically and functionally distinct subset of mature peripheral blood NK cells. To further characterize this subset of NK cells functionally, their potential to express mRNA for the IL-2R and various cytokines after IL-2 activation was examined. Highly purified normal human peripheral blood resting NK (R-NK) cells were obtained by negative immunoselection using OKT3 mAb and magnetic beads coated with goat anti-mouse Ig. By two-color flow cytometry, > 90% of these R-NK cells were either CD3-CD56+CD16+ or - or CD3-CD56-CD16+. R-NK cells were activated in the presence of 6000 IU/ml (22 nM) of IL-2 for different periods of time. After 1, 3, 5, or 24 h, plastic-adherent (A) and nonadherent (NA) NK cells were separated and compared for the expression of the IL-2R or cytokine mRNA by in situ hybridization, using 35[S]-cDNA probes. Only low proportions of R-NK cells expressed genes for IL-2Rp55 (16%) or cytokines IL-2 (20%), IFN-gamma (18%), TNF-alpha (16%), and TGF-beta (7%). Thus, the genes for the IL-2Rp55 and these cytokines were not constitutively expressed by most human R-NK cells, and there was no indication that the NK cells used in these experiments were activated in vivo or during the purification procedure. However, larger proportions of R-NK cells showed expression of mRNA for IL-1-beta (35%) and IL-6 (40%), which indicates that genes for these cytokines may be constitutively expressed in a substantial proportion of normal human circulating NK cells. When R-NK cells were incubated in the presence of 22 nM of IL-2 for 1 to 24 h and separated into A-NK cells and NA-NK cells, a large proportion of A-NK cells became positive for IL-2R and cytokine gene expression. In contrast, the proportion of mRNA-positive NA-NK cells was similar or lower than that observed for R-NK cells, with the exception of an increase in TGF-beta. Thus, significantly higher proportions of A-NK than NA-NK cells expressed mRNA for the IL-2Rp75 (e.g, at 3 h after induction with IL-2, 58% vs 12%), IL-2Rp55 (at 5 h, 74% vs 4%), IL-2 (at 5 h, 68% vs 10%), TGF-β (at 5 h, 82% vs 30%), IL-1-β (at 5 h, 80% vs 24%) and IL-6 (at 5 h, 79% vs 34%). Message for TNF-α or IFN-γ was expressed in a high proportion of both A-NK and NA-NK cells (at 3 h, 70% and 64% for TNF-α and 58% and 30% for IFN-γ, respectively). The increased mRNA expression in A-NK cells at 3 h was followed by high levels of release of the proteins in 48 h culture supernatants. As expected, A-NK cell supernatants contained considerably higher levels of slL-2R, IL-2, and IL-1-β than those of NA-NK cells. In contrast, NA-NK cell supernatants contained more IFN-γ than those of A-NK cells. Both subsets of NK cells produced similar levels of TNF-α. The data indicate that A-NK cells are a subset of NK cells that have not only been rapidly altered in their adherence properties, but also have a high level of NK activity and are selectively activated for expression of IL-2R and several cytokine genes. Thus, A-NK cells appear to represent both a rapidly adherent and activated subset of NK cells.
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Vitolo et al. (1993) studied this question.