Inhibitory activity of fenoterol on Dermatophagoides-, Parietaria-, tetanus-toxoid-, and Candida albicans-stimulated blood mononuclear cells: Differences in β2-adrenoreceptor stimulation but not in cell apoptosis

β₂-adrenoreceptor agonists have the ability to downregulate in vitro the proliferative response of peripheral blood mononuclear cells (BMCs). This activity could be related to a variety of β₂-adrenoreceptor-mediated functions, including induction of cell apoptosis in activated T-cells. To test this hypothesis, BMCs from atopic subjects, sensitized to house dust mites (Dermatophagoides [Der p]) and/or to Parietaria were incubated with fenoterol (10^-8-10^-5 M) in the presence of (a) purified allergen extracts (Der p [5 μg/mL] or Parietaria [5 μg/mL]) or (b) antigens (tetanus toxoid [1 μg/mL] or Candida albicans [5 x 10⁵ bodies/mL]). The BMC proliferation was assessed by [³H] thymidine incorporation and cell apoptosis was assessed by evaluating DNA fragmentation by a fluorescence technique, using propidium iodide. In cultures stimulated with Der p or with Parietaria, fenoterol induced a dose-dependent inhibition of BMC proliferation, significant also at the lowest concentration tested (10^-8M) (p <0.05, each comparison). In contrast, the inhibitory activity of the drug on tetanus-toxoid-stimulated BMCs was significant only at the highest dose tested (10^-5M) (p <0.05), whereas no effect was seen when BMCs were stimulated with C. albicans extract (p > 0.05). The different inhibitory efficacy of fenoterol appeared to be related to the degree of activation of β₂-adrenoreceptors on the different BMC populations that responded to the different stimuli. Indeed, in the presence of fenoterol (10^-6 and 10^-5M), a significant increase in cyclic adenosine monophosphate (cAMP) levels was seen in Der p- or Parietaria- stimulated cells (p <0.05; each comparison), but not in cell cultures stimulated with tetanus toxoid or with C. albicans extracts (p > 0.05; each comparison). Finally, the percentage of cells with fragmented DNA was lower in cultures stimulated with Der p or Parietaria than in those stimulated with tetanus toxoid or C. albicans, and the presence of fenoterol did not modify cell apoptosis (p > 0.05; each comparison). Thus, the different inhibitory activity of fenoterol on BMCs activated by allergens (Der p or Parietaria) or by antigens (tetanus toxoid or C. albicans) seems to be related to differences in β₂-adrenoreceptor expression and/or function in the different antigen-specific T-cell subsets, but it is not influenced by changes in cell apoptosis.