ABSTRACT
Background As longβwave ultraviolet (UV) radiation penetrates the dermis, connective tissue cellular components and circulating blood cells can be possible targets for solar UVA. Basophils, involved in the effector phase of the inflammatory response, play a part in skin diseases such as chronic urticaria, psoriasis, atopic dermatitis, fixed drug eruption, allergic contact dermatitis, urticaria pigmentosa, systemic sclerosis and bullous pemphigoid.
Objective The evaluation of the in vitro effect of UVA on histamine release from human basophils.
Methods Basophils from healthy human volunteers were irradiated, respectively, with UVA at doses of 2.5, 5, 7.5, 10, 20 and 50Β J/cm^2^ and then incubated with an antiβIgE serum. A fluorimetric technique was employed to determine histamine release from samples: (i) incubated with 2% HClO~4~ (complete lysis of basophils); (ii) irradiated with increasing doses of UVA; and (iii) unirradiated (controls).
Results Histamine release was: 100% for HClO~4~ incubated basophils, 30% for unirradiated and antiβIgE incubated cells (controls) and 27%, 24%, 34%, 41%, 60% and 70% for basophils irradiated with UVA doses, respectively, of 2.5, 5, 7.5, 10, 20 and 50Β J/cm^2^ and incubated with antiβIgE. Histamine releasability from irradiated samples was statistically significant (PΒ <Β 0.05), in comparison with controls, at UVA doses equal to 5, 10, 20 and 50Β J/cm^2^.
Conclusions UVA exerts, at least in vitro, a biphasic doseβdependent action on histamine release from human basophils incubated with an antiβIgE serum: at the lowest irradiation doses (<Β 5Β J/cm^2^) it exerts an inhibitory effect and at the highest doses (Β 10Β J/cm^2^) histamine release increases significantly.