The effect of ethidium bromide on the response of spleen explants of primed rabbits to sheep red cells (SRC).

Ethidium bromide (EB) selectively inhibited the response of cultured spleen explants from primed rabbits to SRC. This was particularly so with exposure to relatively high concentrations of the drug for short periods at any time in culture. It was concluded that the likeliest target for the action of EB was the DNA of the cell. The exact nature of this target has not yet been elucidated, but the selectivity and persistence of the inhibition of the development of PFC, as well as lack of morphological evidence of mitochondrial damage suggested DNA of nuclear origin. The prevention, by EB, of increases in the labelling index of cells migrating from explants pre-labelled with [3H]-thymidine, further suggested that, as a result of intercalation with the drug, transfer of DNA, of an episomal nature, was being prevented and that this intercellular exchange was important for the immune response.