The value of synthetic peptides as vaccines for eliciting T-cell immunity

Immunity against Yersinia enterocolitica by vaccination with Yersinia HSP60 immunostimulating complexes or Yersinia HSP60 plus interleukin-12

Microbial heat shock proteins (HSP) are dominant antigens for the host immune response. Because of the high sequence homology between mammalian and microbial HSP, their value as component of a subunit vaccine has been the subject of controversy. Previous work from this laboratory, however, demonstrated for the first time that the adoptive transfer of HSP60-reactive CD4+ alphabeta T-cell clones confers protection against bacterial infection in mice but does not induce autoimmunity. In the present study, we have therefore evaluated the potential role of Yersinia HSP60 (Y-HSP60) as a vaccine in the Yersinia enterocolitica mouse infection model. For this purpose, immunostimulating complexes (ISCOM) which included Y-HSP60 were constructed. Parenteral administration of this vaccine induced high Y-HSP60-specific serum antibody responses as well as T-cell responses. This reaction was parallelled by immunity against a lethal challenge with Y. enterocolitica. In contrast, mucosal application of Y-HSP60-ISCOM failed to induce systemic Y-HSP60-specific T-cell responses and thus failed to induce immunity against yersiniae. Likewise, vaccination with purified recombinant Y-HSP60 induced antibody responses but only weak T-cell responses. Therefore, this vaccination protocol was not protective. However, when interleukin-12 was used as an adjuvant, purified Y-HSP60 induced significant Y-HSP60-specific T-cell responses and thus induced protection against subsequent challenge with yersiniae. These studies suggest that (i) microbial HSP might be promising candidates for the design of subunit vaccines and (ii) interleukin-12 is an efficient alternative adjuvant to ISCOM particles for induction of protective CD4 Th1-cell-dependent immune responses against bacterial pathogens.

Extreme fitness differences in mammalian and insect hosts after continuous replication of vesicular stomatitis virus in sandfly cells

Continuous, persistent replication of a wild-type strain of vesicular stomatitis virus in cultured sandfly cells for 10 months profoundly decreased virus replicative fitness in mammalian cells and greatly increased fitness in sandfly cells. After persistent infection of sandfly cells, fitness was over 2,000,000-fold greater than that in mammalian cells, indicating extreme selective differences in the environmental conditions provided by insect and mammalian cells. The sandfly-adapted virus also showed extremely low fitness in mouse brain cells (comparable to that in mammalian cell cultures). It also showed an attenuated phenotype, requiring a nearly millionfold higher intracranial dose than that of its parent clone to kill mice. A single passage of this adapted virus in BHK-21 cells at 37 degrees C restored fitness to near neutrality and also restored mouse neurovirulence. These results clearly illustrate the enormous capacity of RNA viruses to adapt to changing selective environments.

Pestiviruses: a review

Pestiviruses comprise a group of economically important animal pathogens, namely hog cholera, bovine viral diarrhoea and border disease viruses. The viruses are serologically closely related and share a common host spectrum, i.e. pigs and numerous domestic and wild living ruminants. Interspecies transmissions occur frequently. Despite some common features in their natural hosts, pathogenesis of pestivirus-induced disease is complex; especially some aspects of highly fatal mucosal disease of cattle are still enigmatic. Pestiviruses are amongst the smallest enveloped single-stranded RNA viruses with an icosaeder-shaped nucleocapsid. They are currently classified as Togaviridae. However, based on recent progress in the molecular characterisation of the viruses their taxonomic real-location seems inevitable. Viral RNAs studied so far display one large open reading frame and in infected cells no subgenomic RNA is demonstrable. Structural proteins are coded for by genes located at the 5' end of the RNA. The majority of the genome codes for 2-3 nonstructural proteins. Virions are composed of a major and one minor envelope glycoprotein with molecular weights of 53 and 48 kD respectively. The core is composed of a small protein with a molecular weight of 20 kD. Analysis of viral proteins with monoclonal antibodies has yielded detailed information about the antigenic composition of both structural and nonstructural proteins.