Specific immunity and nonspecific resistance to infection: listeria, protozoa, and viruses in mice and hamsters,.

Specific immunity developed by mice against protozoan (Toxoplasma gondii and Besnoitia jellisoni) and bacterial (Listeria monocytogenes) infections was compared with nonspecific protection conferred by prior infections. The results indicated that homologous immunity protected mice from more than 10-5 LD50 of T. gondii or B. jellisoni, but from only 10-2 LD50 of L. monocytogenes. Heterospecific protection among these organisms was for 10-0.4 minus 10-1.2 LD50. In studies in hamsters specific immunity to protozoan (T. gondii and B. jellisoni) and viral (equine Herpesvirus type 1 and Oriboca virus) infections was compared with nonspecific protection conferred by prior infections with several heterospecific agents: T. gondii; B. jellison; equine Herpesvirus type 1; Oriboca, Ossa, vesicular stomatitis, yellow fever, and Newcastle disease viruses; L. monocytogenes; and the bacillus Calmette-Guerin strain of Mycobacterium tuberculosis. The results indicated that homologous immunity in hamsters was effective against 10-6 minus 10-7 LD50 of T. gondii, B. jellisoni, equine Herpesvirus type 1, or Oriboca virus. Prior infection with Newcastle disease virus protected (probably by interferon induction) against 10-3 LD50 of equine Herpesvirus type 1. Heterospecific protection among other agents was for less than 10 LD50. This insignificant heterospecific protection in infections in which cellular immunity plays a role suggests that both the induction phase and the expression phase are specific.