UC Irvine

ALLOGRAFT immunity and delayed hypersensitivity reactions are caused chiefly by the action of host immune lymphoid cells1. Although these reactions have been much studied in vivo and in vitro, the mechanism of cell destruction is essentially unknown. There have been reports from this laboratory that a cell-free toxic factor released by immune and phytohaemagglutinin (PHA)-stimulated non-immune mouse lymphocytes is essential in the in vitro destruction of target L cells2. This factor, termed lymphotoxin (LT), caused in vitro cytolysis of both continuous and primary cells obtained from many animal species3. Later work showed that lymphocytes from various animal species, including man, could be stimulated in vitro to release LT, in the absence of target cells, by treatments which induce lymphocyte transformation, that is the mixed lymphocyte reaction, PHA and xenogeneic antibody4. It was therefore of interest to investigate whether lymphoid cells obtained from animals with delayed hypersensitivity to soluble antigens could be induced in vitro to release LT-like materials. We wish to report here that in the case of tuberculin hypersensitivity in mice, guinea-pigs and man, non-specific toxic materials are released when the cells are cultured in the presence of specific antigen. © 1969 Nature Publishing Group.