Numeration of DTH-mediating T lymphocytes in mice under optimal titration conditions.

The magnitude of the delayed-type hypersensitivity (DTH) reaction observed in appropriately immunized mice appears to be dependent on an early non-specific inflammatory reaction. The volume of injection and dose of antigen are two major components of this early reaction. The determination of optimal conditions for revealing the DTH reaction enabled definition of a titration method for DTH-mediating T lymphocytes. Injection of a subinflammatory dose of antigen led to conditions of limiting dilution analysis. Thereafter, the initiation of DTH reaction by local injection of a minute number of sensitized cells mixed with an optimal dose of antigen allowed in vivo titration of sensitized T lymphocytes. Single-hit linear curves were obtained when the percentages of negative transfers were plotted against the number of transferred cells in the classical semi-log plot of Poisson's distribution. Initiation of reaction by a quantal mechanism and results giving a linear plot (a single cell type being diluted out) served as an indication that a numeration of sensitized T cells had been performed for the more diluted concentrations of cells assayed.