The duration of contact photosensitivity to TCSA in the mouse.

We examined the course and duration of contact photosensitivity (CPS) to 3,3', 4',5-tetrachlorosalicylanilide (TCSA) in BALB/cJ mice. The doses of TCSA and UVA at sensitization and challenge were kept constant and the time between sensitization and challenge was varied between 4 days and 9 weeks. A small increase in ear swelling was seen at the 4-d challenge with a further increase at 5 d. The peak challenge response was reached at 7 d. Gradually decreased reactions were found at challenges 2,3 and 5 wk after sensitization and, at 7 and 9 wk challenges, sensitization was not detected. Resensitization of the 9-wk group, with challenge a week later, produced a good reaction though not a maximum one, thus the waning of sensitization was not due solely to active suppression.