Akehisa Shichijo

Protection against rabies in mice by a cytotoxic T cell clone recognizing the glycoprotein of rabies virus

By the use of liposomes containing the purified surface glycoprotein (G) of rabies virus and the haemagglutinin-neuraminidase (HN) and fusion (F) glycoproteins of Sendai virus, the target antigen of anti-rabies virus cytotoxic T lymphocyte (CTL) clones isolated in a previous study was identified as the G protein. Recognition of the H-2K determinant of the class I major histocompatibility complex (MHC) was necessary for target lysis by the CTL clones. One of the CTL clones was examined for the ability to protect mice against a lethal rabies virus infection. CTL were transferred into syngeneic mice which had been infected in the hind footpad with the ERA strain of rabies virus. The infection was converted into a lethal infection by cyclophosphamide treatment 1 day after virus infection. Transfer of CTL 2 to 3 days after virus infection protected approximately 50% of mice during the observation period of 4 weeks. Greater protection was obtained in mice receiving both anti-rabies virus antibodies and CTL cells.

Suppression of Cell-Mediated Immunity by Street Rabies Virus Infection

An attempt to define a severe suppression of cell‐mediated immunity by street rabies virus infection was undertaken by using the mice lethally and peripherally infected with a street rabies virus (1088 strain). The cell‐mediated cytotoxic (CMC) activity of the spleen cells from those mice once slightly increased until day 4 after infection but declined rapidly thereafter until their death on days 10 to 12 after infection. In parallel with a decrease of CMC response of the spleen cells from 1088‐infected mice, proliferative response to Con A, IL‐2 activity in the culture supernatants of Con A‐induced proliferation, responsiveness to exogenously added IL‐2 and to Con A to express IL‐2R, of those cells became suppressed, and the marked decrease of the total number of spleen cells was observed. Selective depletion of CD4+ and CD8+ cells in the spleens, abnormalities of IL‐1 and E‐type prostaglandins (PGE2) production or production of inhibitory component able to block IL‐2 activity by spleen cells were not observed and these factors did not appear to be associated with the suppression of proliferative response to Con A. However, an apparent association of CD8+ cells in the suppression of differentiation of pre‐cytotoxic lymphocytes (CTL) into CTL was demonstrated in the co‐culture experiments of the spleen cells from 1088‐infected mice with spleen cells of mice infected with an attenuated rabies virus (ERA strain) which can induce higher levels of CMC response. There was no evidence of the productive replication of rabies virus in thymus and spleen of 1088‐infected mice. The relationship of these observations to current theories on virus‐induced immunosuppression was discussed.

A Mouse Model for the Pathogenesis and Postexposure Prophylaxis of Rabies

A mouse model for the study of postexposure prophylaxis of rabies was established. Mice injected intramuscularly with a street strain of rabies virus were significantly protected from death by five daily 0.2‐ml doses of inactivated rabies vaccine of chick embryo cell culture origin initiated immediately or 3 hr after infection. In these mice, a large amount of circulating interferon was induced as early as 1 hr after the first dose of vaccine and lasted until at least 12 hr but no such amount of interferon was induced by additional doses of vaccine. Serum antibody was first detected in the mice on day 6. It was noted that some of the surviving mice manifested an ataxia or paralysis of the legs. Increasing mortality rates were shown in mice treated with decreasing doses of the vaccine. Passive protection tests using concentrated IgG and IgM antibodies with equivalent neutralization titers showed that IgG antibody gave total protection when given 24 hr before the infection, while it was almost totally ineffective in reducing the mortality when given 2 days or more after infection. IgM antibody did not protect the mice even when given 24 hr before infection. These results suggest that interferon production is more important than antibody production in the initial stages of protection by postexposure vaccination. However, the mechanisms of postexposure prophylaxis in this model could not be explained only by the interferon produced by the vaccine and the possible contributions of additional mechanisms were suggested.