The demonstration of a phenomenon in vitro applicable to the study of delayed hypersensitivity

Peritoneal exudate cells from guinea pigs with delayed hypersensitivity skin reactions were incubated with the specific antigen and ruptured by freezing and thawing. The supernatant of these ruptured cells was incubated with several primary and established tissue culture strains. Extracts of peritoneal cells from hypersensitive guinea pigs that were incubated with the specific antigen induced the tissue culture cells to overproduce acid in the medium. Similarly, extracts from nonsensitized guinea pigs did not induce a corresponding decrease in pH. The formation of “acid-stimulating activity” required specificity of the reactants because sensitive cells incubated with saline or heterologous antigen did not stimulate the tissue culture cells. “Acid-stimulating activity” was found to be independent of the tissue culture cell strain, the media used to grow the tissue culture cells, and the sensitized peritoneal cell-antigen system. No “acid-stimulating activity” was produced if frozen and thawed cells were incubated with the specific antigen. “Acid-stimulating activity” was produced by peritoneal cells capable of passively transferring delayed hypersensitivity, but not from sera of the same guinea pigs. Sera from sensitized guinea pigs did not confer “acid-stimulating activity” to nonsensitized peritoneal cells. KB tissue cells did not overproduce acid when specific precipitates were added to the media. The degree of hypersensitivity of the guinea pigs donating peritoneal cells corresponded with the ability of these cells to induce acid production in a KB cell culture. Guinea pigs, with lesser sensitivity to skin testing donated cells with lesser “acid-stimulating activity.” It is believed that this phenomenon may be applicable to the measurement in vitro of delayed hypersensitivity uncomplicated by host factors.