Secondary cytotoxic cell response to lymphocytic choriomeningitis virus. III. In vivo protective activity of effector cells generated in vitro.

Secondary cytotoxic T cells were generated by culturing WE3-LCM virus-specific memory CBA/H spleen cells with WE3-LCM virus-infected syngeneic peritoneal cells at 37° for 5 days, and were found to be highly potent in reducing virus titres in the visceral organs of syngeneic recipients when transferred 24 h before intravenous virus challenge (e.g. 3.1×10 cells transferred gave approximately 3 logs reduction of virus titre). Protection was measured by titrating spleens for virus in a plaque assay, usually 2 days post virus-challenge. Intravenously administered secondary effectors did not, however, elicit a reduction in brain virus titres by 3 days after intracerebral inoculation of virus. Cells mediating protection were sensitive to treatment with anti-θ ascitic fluid plus complement. Protection occurred only when donors of secondary cells, infected stimulator cells and recipients shared -2 or -2, and there was a similar genetic restriction for these effectors to efficiently lyse virus-infected targets . Spleen cells from ectromelia virus-memory mice were cultured with ectromelia virus-infected syngeneic peritoneal `stimulator' cells and generated secondary effector cells which protected syngeneic recipients from subsequent challenge with ectromelia but not LCM virus. However, secondary effector cells derived from stimulation of spleen cells from WE3-LCM virus-memory mice with WE3-LCM virus-infected syngeneic stimulator cells caused a significant reduction in spleen virus titres in syngeneic recipients challenged with either ectromelia or LCM virus. If WE3-LCM virus-infected stimulator cells were fixed and responder spleen cells were either from very old (6–12 months post-priming) WE3-LCM virus-memory mice, or from ARM-LCM virus-memory mice, this unidirectional cross-protection of ectromelia virus-challenged mice was less pronounced. One explanation for the unidirectional cross-protection was that the transferred secondary effectors contained and released infectious LCM virus (or defective virions) which adsorbed to recipients' spleen cells; these latter cells displayed both LCM and ectromelia virus-specific antigenic patterns after ectromelia virus challenge, rendering them susceptible to specific T-cell mediated lysis. Clear specificity of effector cells was demonstrated at the effector: target level between LCM virus and ectromelia virus. (Experiments to compare the activity of secondary effectors with primary effector T cells raised or were hampered because of the large amounts of infectious virus in the latter two populations.) Secondary effectors reduced spleen, lung and liver virus titres when transferred 24 h after virus challenge, but were less efficient in protecting recipients than when given before virus.