RESPONSIVENESS OF HUMAN SKIN MAST-CELLS TO REPEATED ACTIVATION - AN IN-VITRO STUDY

To assess human mast-cell (MC) behavior after repetitive activation, w e cocultured human foreskin MC (SMC) with human foreskin fibroblasts ( F). Under these conditions, we have previously demonstrated that SMC k eep their viability and functional activity for up to 8 days. SMC were presensitized with atopic serum and repeatedly activated by consecuti vely increasing concentrations of anti-IgE antibodies (alpha-IgE, 0.00 02-0.1%). This treatment, which mimics the ''rush desensitization'' pr ocedure, led to complete SMC unresponsiveness to activation by alpha-I gE at optimal concentrations, as evaluated by histamine release. Howev er. presensitization of SMC with IgE antibodies before exposure to alp ha-IgE restored their sensitivity to this stimulus. These data indicat e that desensitization was probably due to lack of membrane-hound IgE rather than to downregulation of intracellular mechanisms. In fact. SM C challenged by an optimal concentration of alpha-IgE could release hi stamine upon a second activation by 2 h after the first activation. if the cells had been presensitized before the second challenge. SMC inc ubation with increasing concentrations of compound 48/80 (0.2-10 mu g/ ml) led to MC unresponsiveness to an optimal concentration of this sti mulus. Furthermore. SMC activated by an optimal concentration of compo und 48/80 and rechallenged with the same agent were insensitive to the second activation for al least 24 h. In summary, we have shown that i t is possible to induce ''desensitization'' in SMC to both IgE-depende nt and IgE-independent stimuli by incubating the cultures with consecu tively increasing concentrations of the activator. SMC can release his tamine when reactivated with alpha-IgE antibodies after presensitizati on by reactivation with compound 48/80 in only 2-3 days.