CD4 and infection: Similarly, CD4+ T cells have been found essential for maintaining a robust or protective cytotoxic T cell memory response upon vaccination with recombinant VACV expressing lymphocytic choriomeningitis virus glycoprotein, or upon infection of mice with Listeria monocytogenes bacteria [81], [82], [83] The possibility that clearance of ECTV cannot be accomplished because of the absence of T helper cell dependent antibody responses appears unlikely in the view of the fact that CD4-depleted animals still mounted substantial levels of VACV-specific antibodies.