Suppression of delayed hypersensitivity by measles virus infection in guinea pigs

Cell surface activation of the alternative complement pathway by the fusion protein of measles virus

Measles virus (MV)-infected cells are activators of the alternative human complement pathway, resulting in high deposition of C3b on the cell surface. Activation was observed independent of whether CD46 was used as a cellular receptor and did not correlate with CD46 down-regulation. The virus itself was an activator of the alternative pathway and was covered by C3b/C3bi, resulting in some loss in infectivity without loss of virus binding to target cells. The cell surface expression of MV fusion (F), but not haemagglutinin, envelope protein resulted in complement activation of the Factor B-dependent alternative pathway in a dose-dependent manner and F-C3b complexes were formed. The underlying activation mechanism was not related to any decrease in cell surface expression of the complement regulators CD46 and CD55. The C3b/C3bi coating of MV-infected cells and virus should ensure enhanced targeting of MV antigens to the immune system, through binding to complement receptors.

Development of a new type of influenza subunit vaccine made by muramyldipeptide-liposome: enhancement of humoral and cellular immune responses

The muramyldipeptide (MDP), [6-O-(2-tetradecyl-hexa-decanoyl)-N-acetylmuramyl-L-isoglutamine] can be incorporated into liposomes with haemagglutinin and neuraminidase subunits were attached to the inner and outer surfaces of lamellar structures of the liposomes, probably through their hydrophobic ends. The addition of cholesterol resulted in much more stable liposomes, which were similar in size and shape to native influenza virus particles. These liposomes enhanced the immunogenicity of haemagglutinin in mice, such that the levels of antibody induced were about 16-fold higher than those of subunit haemagglutinin vaccine alone. Results of proliferation tests with spleen cells from mice and guinea-pigs were consistent with the immunopotentiation of haemagglutinin by liposomes. In addition, the higher antibody levels produced in mice, immunized with the haemagglutinin and MDP-containing liposomes (MDP-virosomes), were maintained for at least 6 months. Enhancement of the cellular immune response, measured by delayed type hypersensitivity reactions, was also observed in the guinea-pigs immunized with MDP-virosome vaccine. Preliminary tests with splenocytes from mice immunized with different vaccines also indicated that the MDP-virosome vaccine induced cytotoxic T-cell activity in these mice. This study revealed that the formation of liposomes with muramyldipeptide enhanced the level and persistence of circulating antibody, and enhanced cellular immunity in guinea-pigs and mice.