The induction of photocontact sensitivity in guinea pigs without UVB radiation

Allergic photocontact sensitization could be induced in guinea pigs with 3,3',4',5-tetrachlorosalicylanilide (TCSA), 3,4',5-tribromosalicylanilide (TBS), and bithionol using pretreatment with sodium lauryl sulfate (SLS) and long-wave ultraviolet (UVA) radiation. Mid-wave ultraviolet below 320 nm (UVB) was not necessary for the induction of sensitization. Combined use of SLS pretreatment with UVA radiation resulted in more effective sensitization than combined UVB and UVA radiation. Higher sensitization rates to TCSA and TBS were achieved by allowing rest periods between each of 5 2-hr exposures to UVA than by daily 1-hr exposures for 10 consecutive days. The opposite result was obtained with bithionol. Although UVB has been customarily used in the past for induction of photosensitivity, its role is only to irritate the site of induction.