Microarray analysis reveals previously unknown changes in Toxoplasma gondii-infected human cells

Genetic approaches to studying virulence and pathogenesis in Toxoplasma gondii

Toxoplasma gondii is a common protozoan parasite that causes disease in immunocompromised humans. Equipped with a wide array of experimental tools, T. gondii has rapidly developed as a model parasite for genetic studies. The population structure of T. gondii is highly clonal, consisting of three distinct lineages that differ dramatically in virulence. Acute virulence is probably mediated by the genetic differences that distinguish strain types. We have utilized a combination of genetic approaches to investigate the acute virulence of toxoplasmosis using the mouse model. These studies reveal the surprising finding that pathogenicity is due to the over-stimulation of normally protective immune responses. Classical genetic linkage mapping studies indicate that genes that mediate acute virulence are linked to chromosome VII in the parasite. To increase the resolution of genetic mapping studies, single-nucleotide polymorphisms are being developed based on an extensive database of expressed sequence tags (ESTs) from T. gondii. Separately, DNA microarray studies are being used to examine the expression of parasite and host genes during infection. Collectively, these approaches should improve current understanding of virulence and pathogenicity in toxoplasmosis.

Immediate/early response to Trypanosoma cruzi infection involves minimal modulation of host cell transcription

Host cell infection by the intracellular pathogen, Trypanosoma cruzi, involves activation of signaling pathways, cytoskeletal reorganization, and targeted recruitment of host cell lysosomes. To determine the consequences of T. cruzi invasion on host cell gene expression, high density microarrays consisting of approximately 27,000 human cDNAs were hybridized with fluorescent probes generated from T. cruzi-infected human fibroblasts (HFF) at early time points following infection (2-24 h). Surprisingly, no genes were induced > or =2-fold in HFF between 2 and 6 h post-infection (hpi) in repeated experiments while immediate repression of six host cell transcripts was observed. A significant increase in transcript abundance for 106 host cell genes was observed at 24 hpi. Among the most highly induced is a set of interferon-stimulated genes, indicative of a type I interferon (IFN) response to T. cruzi. In support of this, T. cruzi-infected fibroblasts begin to secrete IFNbeta at 18 hpi following the induction of IFNbeta transcripts. As compared with global transcriptional responses evoked by other intracellular pathogens, T. cruzi is a stealth parasite that elicits few changes in host cell transcription during the initiation of infection.

Genomics and future biological weapons: the need for preventive action by the biomedical community

There is an increasing concern within both the scientific and security communities that the ongoing revolution in biology has great potential to be misused in offensive biological weapons programs. In light of the 11 September tragedy, we can no longer afford to be complacent about the possibility of biological terrorism. Here we review the major relevant trends in genomics research and development, and discuss how these capabilities might be misused in the design of new bioweapons. We also discuss how the breakthroughs that have come from the genomics revolution may be used to enhance detection, protection and treatment so that biological warfare agents are never used.