Complement cleavage products in the phototoxic reaction of porphyria cutanea tarda.

We have measured C3, C4, CH50 and complement cleavage products C3a and C5a in in sera and plasma from PCT patients and normal controls 10 min and 1, 4 and 24 h after UVA irradiation. We found elevated C3a concentrations in PCT patients immediately after UVA irradiation and 24 h later. The same was true for CH50, whereas C3, C4 and C5a did not change significantly. No such changes occurred in normal controls. Our data suggest that activation of the complement cleavage product C3a by porphyrin and UV light triggers a series of events that cause tissue damage.