The use of plasmid DNA encoding influenza viral proteins to vaccinate animals constitutes a promising approach to the development of effective subunit vaccines. This review describes the results obtained by the immunization of mice with such plasmid DNAs. (i) Both hemagglutinin (HA)- and neuraminidase (NA)­ expressing DNAs for the surface glycoproteins from A/PR/8/34 (H1N1) or B/lbaraki/2/85 virus can provide the most effective protection against influenza A-type or B-type virus infection among the various viral protein-expressing DNAs tested in BALB/c mice. (ii) A mixture of plasmid DNAs encoding HA and NA can provide more effective protection against virus challenge than plasmid DNA encoding HA or NA alone in BALB/c mice. (iii) NA-DNA can provide protection against infection not only by homologous virus but also by drift viruses. (iv) HA-DNA from A/PR/8/34 (H1N1) virus provides significant protection only in BALB/c (H-2^b) mice, whereas HA-DNA from B/Ibaraki/2/85 virus affords significant protection in BALB/c, BIO (H-2^d), and C3H (H-2^k) mice. NA-DNA from both A-type and B-type viruses provides significant protection in the three strains of mice. These results suggest that both HA and NA molecules should be used as vaccine components to provide effective protection against influenza A-type and B-type virus infection in genetically heterogeneous humans.

Amebiasis is epidemic in two major populations in Japan: male homosexuals and institutionalized people. Currently available diagnostic, chemotherapeutic, and prophylactic measures and their problems are discussed. Recent advances in basic research on amebiasis are also described with new findings of unique metabolisms and intracellular structures and organization. Discoveries and analyses of the unique features presented by this parasitic protist help in our elucidation of the pathogenic mechanisms of the parasite and may eventually lead to the development of new drugs and vaccines against amebiasis.

Infection with Toxoplasma gondii is of medical importance in relation to a recent increase in cases of acquired immunodeficiency syndrome (AIDS). In the present study, we surveyed antibody to Toxoplasma among 1,761 people in Surabaya, Indonesia. The overall prevalence was 58% with significant differences between males (63%) and females (52%; P < 0.001). Although antibody prevalences at 0-9 years in both genders were less than 10%, those at ages over 10 years were more than 50% in males or more than 40% in females, suggesting an extremely high transmission rate of the parasite to humans in this area. A bimodal pattern in the frequency distribution of Toxoplasma antibody levels suggested a persistent feature of Toxoplasma infection in humans.