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.(ABSTRACT TRUNCATED AT 400 WORDS)