Once logged-in, VirHostNet users can directly query the knowledge base by using a wide range of information concerning viral (e.g. NCBI protein name or accession number) or human proteins (e.g. ENSEMBL gene or protein accession number, NCBI gene name, REFSEQ protein accession number and UNIPROT primary and secondary accession numbers) ( Figure 4A ). AJAX technology was incorporated to control protein name and accession number availability in VirHostNet. Another important feature of the interface is batch query. It allows in-depth analysis of interaction profiles with cellular and/or viral proteins from a list of proteins defined for instance in high-throughput studies (microarray, yeasttwo hybrid). A list of genes or proteins of interest can also be assessed by the mean of contextual information, such as taxonomical information, Gene Ontology terms, KEGG pathways and INTERPRO protein domains. These properties offer a unique access to protein-protein interaction networks: (i) associated to a specific virus taxon or (ii) underlying canonical sub-cellular localization, cellular functions and pathways.