Induction of Suppressor T Cells and Inhibition of Contact Hypersensitivity in Mice by 12-O-Tetradecanoylphorbol-13-Acetate and Its Analogs

12-O-tetradecanoylphorbol-13-acetate (TPA) and its analogs were surveyed for their abilities to modify contact hyper-sensitivity (CHS) responses in SENCAR mice. Sensitization of dorsal skin with 2,4-dinitrofluorobenzene (DNFB) and subsequent challenge of the ear 5 d later resulted within 24h in ear swelling and increased vascular permeability (as measured by the extravasation of Evans Blue dye). Treatment of dorsal or ventral skin with TPA 4 times (application made every 3 or 4 d) prior to sensitization on the dorsum inhibited subsequent induction of CHS by DNFB challenge. Maximum suppression of CHS required sensitization at the site of TPA treatment. Suppression occurred over a narrow dose range of TPA (0.1–1.0 μg), and qualitatively correlated with the tumor incidences scored in an initiation-promotion multistage skin carcinogenesis experiment. Multiple applications (4×) of the promoters phorbol-12.13-dibenzoate (10 μg) and mezerein (2 μg) also suppressed CHS, whereas the non-promoter phorbol (20 μg) and the first stage tumor promoter 4-O-methyl TPA (20 μg) had no effect. Adoptive transfer of splenocytes isolated from mice pre-treated with TPA prior to DNFB sensitization inhibited the development of CHS in recipient mice that were sensitized and challenged with DNFB, but not oxazolone. Splenocyte preparations depleted of T lymphocytes prior to transfer could not suppress CHS in recipient mice. Conversely, suppressive activity was concentrated in splenocyte preparations depleted of adherent cells/monocytes. Collectively, these studies demonstrate that TPA treatment of murine epidermis prior to sensitization with hapten can inhibit subsequent hapten-dependent elicitation of CHS. This suppression is mediated in part by antigen-specific suppressor T cells. Furthermore, there is a qualitative correlation between the complete and second stage in vivo tumor-promoting activities of TPA and its analogs, and their abilities to inhibit CHS.