Lymphocyte-mediated cytotoxicity to cells infected with measles virus: I. Use of in vitro infected leukocytes as autologous target cells; absence of virus-specific cytotoxic lymphocytes

We investigated lymphocyte-mediated cytotoxicity in humans to autologous cells infected with measles virus. Mononuclear leukocytes, isolated from peripheral blood, were stimulated by phytohemagglutinin (PHA) and infected with measles virus. At 72 hr after infection, about 80% of the cells could be lysed by antibodies against measles virus and human complement, which meant that at that time the expression of virus-specific antigens on the cell surface was maximal. Such PHA-stimulated, infected leukocytes were used as target cells in an assay for lymphocyte-mediated cytotoxicity. Effector lymphocytes were obtained from the same donor who had provided the target cells, and were tested for their cytotoxicity directly after isolation.Lymphocytes obtained from adult humans, with a history of natural measles infection contracted during childhood, were not found to be cytotoxic to autologous infected cells, unless antibodies against measles virus were present during the assay. The same response, though to a lesser extent, was observed with cord blood lymphocytes obtained from healthy neonates. This indicates that the observed cytotoxicity does not reflect acquired cellular immunity but rather antibody-dependent cellular cytotoxicity (ADCC).