A kinetic approach to cellular interaction in delayed-type hypersensitivity

The virus plaque assay for enumerating antigen-sensitive cells in delayed-type hypersensitivity has been employed in a kinetic analysis of cell interaction in vitro. When cultures are initiated at varying cell densities of tuberculin-sensitive guinea pig, or human lymphocytes, and logarithmic plots of the cell dose versus response in virus-plaque-forming cells are made, the slopes of the resulting lines indicate theoretically the number of cellular interactions required to produce an observable virus plaque-forming cell. In control cultures, i.e., sensitized lymphocytes cultured in the absence of antigen, or non-sensitized lymphocytes cultured in the presence or absence of tuberculin, the number of cells able to produce virus plaques varied directly proportionately with the number of cells cultured (m = 1), and constitute the background. In contrast, in the case of sensitized human peripheral blood lymphocytes or guinea pig lymph node cells stimulated by tuberculin, the average slope was found to be two (m = 2), indicating that interaction of two cells was required to produce one virus plaque-forming cell. When increasing concentrations of sensitized lymphocytes were diluted with syngeneic unsensitized cells, the results indicated that only one of the interacting cells was specific for antigen. Removal of a glass-adherent population diminished the number of plaque-forming cells, and reconstitution of purified glass-adherent cells was partially able to restore the activity. These results are consistent with the view that activation of lymphocytes by specific antigens requires two cells, one of which has specificity, the other of which acts non-specifically and is glass-adherent.