Suppression of the antibody response by phorbol esters in the mouse is due to an effect on the nylon wool adherent cell population.

Phorbol esters, in particular 12-O-tetradecanoyl-phorbol-13-acetate (TPA), have been shown to have profound effects on most biological systems including tumor promotion. Presented here are studies on the acute toxic effects of TPA, and the effects of phorbol esters on the in vivo and in vitro, T cell-dependent, antigen-specific antibody response in the mouse. The LD50 of a single i.v. dose of TPA in the mouse was 309 micrograms/kg. Acute toxic effects included lethargy, hypothermia and enlarged, hemorrhagic spleens at the higher doses. TPA was shown to be a potent inhibitor of the in vivo primary antibody response as measured by the IgM antibody-forming cell (AFC) response to sheep red blood cells (sRBC). The ED50 of a cumulative i.v. dose was 145 micrograms/kg administered the day before and the day of immunization (72.5 micrograms/kg/day). A cumulative dose of 500 micrograms/kg (250 micrograms/kg/day) resulted in a 100% suppression of the response. This in vivo exposure to TPA did not alter B cell/T cell ratio in the spleen. Phorbol ester analogs inactive in other biological systems were also inactive in the in vivo AFC response. The in vitro AFC assay was used to determine what cell type was being affected by TPA. Separation of the adherent spleen cells into B and T cell populations was done using nylon wool columns and anti-theta plus complement treatment. Experiments with these cell populations indicated that TPA produced suppression of the response due to an effect on the nylon wool adherent cell population.