Immune response in rabbits to surface components of extracellular and intracellular forms of vaccinia virus.

The development of cellular as well as humoral immune response to extracellular and intracellular forms of vaccinia virus (ECV and ICV, respectively) and their surface antigens were studied in rabbits. Direct lymphocyte cytotoxicity and peripheral blood leukocyte migration inhibition tests were used to measure cell-mediated immune response, while neutralizing and hemagglutination-inhibiting antibodies were assayed for measuring humoral immune response. Direct cytotoxicity of lymphocytes from rabbits immunized with ECV or its surface proteins was demonstrable by day 7 after immunization, and by the end of week 3 it almost declined to pre-immunization levels. Inoculation with ICV or its surface proteins failed to induce lymphocyte cytotoxicity. In contrast, migration inhibition of peripheral blood leukocytes from rabbits immunized with ECV, ICV, or their surface proteins was observed with homologous antigens. However, leukocytes from rabbits immunized with ECV or its surface proteins also showed migration inhibition in the presence of ICV. Similarly, in the humoral immune response, neutralizing antibodies were produced against homologous as well as heterologous forms of virus despite immunization with purified preparations of ECV, ICV, or their surface proteins. Adsorption with purified ICV preparations abolished the neutralizing activity of these antisera against heterologous forms of virus. Hemagglutination-inhibiting antibodies, on the other hand, were produced only after immunization with ECV or its surface proteins. In addition, antibody-dependent cell-mediated cytotoxicity was employed to detect specific antibody response after immunization of rabbits with live virus, ECV, and ICV. Antisera raised against ECV or live virus supported antibody-dependent cell-mediated cytotoxicity, whereas ICV-antiserum failed to do so. The antibody activity present in the former antisera was abolished by absorption with cell membranes from vaccinia-infected cells but not with purified ICV. The data suggest that immunization with inactivated ECV seems to bring about interaction between host immune response (cellular and humoral) and virus-infected cells, which may, perhaps, be necessary for protection against pox virus infection. A similar interaction is unlikely to occur after immunization with inactivated ICV.

Candidacidal activity of mouse macrophages in vitro.

Mouse peritoneal macrophages were infected in vitro with Candida albicans, and the phagocytic and candidacidal activities were estimated by microscopic examination of Giemsa-stained cells. Activated macrophages obtained from either BCG-vaccinated animals or by in vitro exposure of normal macrophages to phytohemagglutinin-induced lymphokines exhibited higher phagocytic and candidacidal activities than did normal macrophages. However, activated macrophages obtained by in vitro exposure of macrophages to candida-induced lymphokines exhibited the highest phagocytic and candidacidal activities. The incorporation of immune mouse serum into the culture medium also enhanced the phagocytic and candidacidal activities of the normal macrophages but failed to improve the function of the activated macrophages. These results suggest that both activated macrophages and antibodies may be required for controlling candida infections in mice.

Use of the 51chromium release test to demonstrate antigenic differences between extracellular and intracellular forms of vaccinia virus.

Complement-dependent antibody lysis of vaccinia-infected cells was examined to demonstrate the antigenic differences between extracellular (ECV) and intracellular (ICV) forms of vaccinia virus. Cytolytic antibodies present in the antisera raised against ECV or live virus (LV) were completely removed by absorption with infected cell membranes or purified ECV but not with purified ICV. Absorption with infected cell membranes also abolished the neutralizing activity of ECV and LV antisera against ECV. On the other hand, antiserum against ICV did not contain cytolytic antibodies against vaccinia-infected cells, even though its neutralizing antibody titre against ICV was high. Moreover, both ECV and ICV antisera neutralized a small proportion of the heterologous form of virus, despite using purified preparations of ECV and ICV, respectively, for raising these antisera in rabbits. In contrast, the 51Cr release test only detected the antibodies against ECV and thus can be used to differentiate between the antibody activity of a serum against ECV and ICV.