Biphasic modulation of apoptotic pathways in Cryptosporidium parvum-infected human intestinal epithelial cells.

The impact of Cryptosporidium parvum infection on host cell gene expression was investigated by microarray analysis with an in vitro model using human ileocecal HCT-8 adenocarcinoma cells. We found changes in 333 (2.6%) transcripts at at least two of the five (6, 12, 24, 48, and 72 h) postinfection time points. Fifty-one of the regulated genes were associated with apoptosis and were grouped into five clusters based on their expression patterns. Early in infection (6 and 12 h), genes with antiapoptotic roles were upregulated and genes with apoptotic roles were downregulated. Later in infection (24, 48, and 72 h), proapoptotic genes were induced and antiapoptotic genes were downregulated, suggesting a biphasic regulation of apoptosis: antiapoptotic state early and moderately proapoptotic state late in infection. This transcriptional profile matched the actual occurrence of apoptosis in the infected cultures. Apoptosis was first detected at 12 h postinfection and increased to a plateau at 24 h, when 20% of infected cells showed nuclear condensation. In contrast, experimental silencing of Bcl-2 induced apoptosis in 50% of infected cells at 12 h postinfection. This resulted in a decrease in the infection rate and a reduction in the accumulation of meront-containing cells. To test the significance of the moderately proapoptotic state late in the infection, we inhibited apoptosis using pancaspase inhibitor Z-VAD-FMK. This treatment also affected the progression of C. parvum infection, as reinfection, normally seen late (24 h to 48 h), did not occur and accumulation of mature meronts was impaired. Control of host apoptosis is complex and crucial to the life of C. parvum. Apoptosis control has at least two components, early inhibition and late moderate promotion. For a successful infection, both aspects appear to be required.

Comparative gene expression by WC1+ gammadelta and CD4+ alphabeta T lymphocytes, which respond to Anaplasma marginale, demonstrates higher expression of chemokines and other myeloid cell-associated genes by WC1+ gammadelta T cells.

The functions of gammadelta T cells are enigmatic, and these cells are often considered as evolutionary remnants of well-characterized alphabeta T cells. However, their conservation throughout evolution suggests that gammadelta T cells are biologically unique. In ruminants, gammadelta T cells expressing the workshop cluster 1 (WC1) scavenger receptor comprise a large proportion of circulating lymphocytes, suggesting these cells are biologically relevant and functionally different from alphabeta T cells. In fact, bovine WC1(+) gammadelta T cells can act as APC for alphabeta T cells, indicating they may express genes encoding proteins associated with innate immunity. The present study was designed to compare immune function gene expression profiles of clonal populations of WC1(+) gammadelta and CD4(+) alphabeta T cells derived from the same animal, which respond to major surface protein 2 (MSP2) of the intraerythrocytic rickettsial pathogen of cattle, Anaplasma marginale. Gene expression profiles of activated T cell clones were compared using a microarray format, and differential gene expression was confirmed by real-time RT-PCR and protein analyses. We demonstrate that although MSP2-specific alphabeta and gammadelta T cell clones express many of the same genes, gammadelta T cell clones express high levels of genes associated with myeloid cells, including chemokines CCL2, CXCL1, CXCL2, CXCL6, and surface receptors CD68, CD11b, macrophage scavenger receptor 1, macrophage mannose receptor, and galectin-3. It is important that many of these genes were also expressed at higher levels in polyclonal WC1(+) gammadelta T cells when compared with CD4(+) alphabeta T cells selected from peripheral blood.

Regulation of apoptotic pathways in bovine gamma/delta T cells.

T lymphocytes bearing gamma/delta TCRs are a major population of T cells in neonatal calves and discrete subsets of gamma/delta T cells display tissue-specific accumulation and responsiveness to infection. To enhance our understanding of the immunobiology of gamma/delta T cells, we characterized the gene expression profile of circulating bovine gamma/delta T cells following stimulation with recombinant human IL-2 and ConA. Statistical analysis of microarray data identified 108 genes with significantly altered expression, including four genes associated with apoptosis. Real-time reverse transcription-PCR (RT-PCR) analysis of 15 genes related to apoptotic pathways showed that both the Fas-mediated and the mitochondrial apoptotic pathways were repressed in circulating bovine gamma/delta T cells in response to mitogen activation, indicating that stimulated peripheral bovine gamma/delta T cells are resistant to activation-induced apoptosis.

Sequential patterns of gene expression by bovine monocyte-derived macrophages associated with ingestion of mycobacterial organisms.

We investigated mechanisms involved in killing of mycobacterial organisms by comparing the response of bovine monocyte-derived macrophages to ingestion of Mycobacterium avium subsp. paratuberculosis or M. avium subsp. avium organisms. Previous studies have shown that bovine macrophages have the capacity to kill M. avium subsp. avium organisms in vitro but cannot kill M. avium subsp. paratuberculosis organisms. We used bovine cDNA microarray technology to investigate sequential gene expression by bovine monocyte-derived macrophages and function assays to correlate gene expression with biological activity. Results of the gene expression studies indicated substantial differences between macrophages phagocytizing the two organisms. At 2, 6, and 24h after infection, 12, 53, and 19 genes, respectively, were differentially expressed. Over all time periods, approximately twice as many genes had lower expression in M. avium subsp. paratuberculosis-infected macrophages than had greater expression. Differentially regulated genes of most interest to antimicrobial responses included inflammatory molecules (transforming growth factor-beta, thrombospondin 1, monocyte chemokine, and cathepsin K), phagosome-lysosome-related genes (H(+) ATPases, lysosomal-associated membrane protein 2, vesicle trafficking protein, and solute carrier protein), and apoptosis-related genes (tumor necrosis factor receptor-associated factor 2, and tumor protein p(53) binding protein). Function assays indicated that M. avium subsp. avium-infected macrophages had a greater capacity to acidify phagosomes and a greater percentage of apoptotic cells. In conclusion, these results suggest that a complex interaction between macrophages and mycobacterial organisms is involved in determining the fate of the organism. Although multiple genes and metabolic pathways are involved, the capacity of cells to acidify phagosomes and induce apoptosis appears to play a prominent role.

Host intestinal epithelial response to Cryptosporidium parvum.

Cryptosporidium parvum is an obligate intracellular protozoan parasite that is a well-recognized cause of diarrhea in humans and animals throughout the world, and is associated with a substantial degree of morbidity and mortality in patients with the acquired immunodeficiency syndrome (AIDS). C. parvum primarily infects epithelial cells of the gastrointestinal tract, resulting in acute watery diarrhea for which there is no effective therapy. During infection, all parasite development, sexual or asexual, occurs within epithelial cells of the host. This requires a unique and complex association between two distinct eukaryotic organisms. Conversely, due to the intracellular nature of C. parvum, epithelial cells appear to play a key role in activating and communicating with the host immune system. Delineation of the biochemical processes that are regulated within infected epithelial cells is crucial for understanding the pathology of C. parvum infection, the process by which the host clears and ultimately develops resistance to infection, and the development of chemotherapeutic strategies to intercede infections.

Complete genome sequence of the apicomplexan, Cryptosporidium parvum.

The apicomplexan Cryptosporidium parvum is an intestinal parasite that affects healthy humans and animals, and causes an unrelenting infection in immunocompromised individuals such as AIDS patients. We report the complete genome sequence of C. parvum, type II isolate. Genome analysis identifies extremely streamlined metabolic pathways and a reliance on the host for nutrients. In contrast to Plasmodium and Toxoplasma, the parasite lacks an apicoplast and its genome, and possesses a degenerate mitochondrion that has lost its genome. Several novel classes of cell-surface and secreted proteins with a potential role in host interactions and pathogenesis were also detected. Elucidation of the core metabolism, including enzymes with high similarities to bacterial and plant counterparts, opens new avenues for drug development.

Cryptosporidium parvum regulation of human epithelial cell gene expression.

Cryptosporidium parvum is an obligate intracellular protozoan capable of causing life-threatening diarrhoeal disease in immunocompromised individuals. Efforts to develop novel therapeutic strategies have been hampered by the lack of understanding of the pathogenesis of infection. To better understand the host response to C. parvum infection, gene expression profiles of infected human ileocecal adenocarcinoma cells were analysed by using Affymetrix oligonucleotide microarrays containing probe sets for 12,600 human genes. Statistical analysis of expression data from three independent experiments identified 223 genes whose expression was reproducibly regulated by C. parvum infection at 24 h post-inoculation (125 up-regulated and 98 down-regulated), 13 of which were validated by quantitative reverse transcriptase polymerase chain reaction analysis. This analysis revealed the consistent up-regulation of host heat-shock genes and genes for pro-inflammatory chemokines IL-8, RANTES, and SCYB5. Multiple genes for host actin and tubulin genes were up-regulated whereas genes for actin binding proteins were down-regulated, confirming previous observations of host cytoskeleton rearrangement in response to C. parvum infection. In addition, host genes associated with cell proliferation and apoptosis were differentially regulated, reflecting the complexity of host-parasite interaction. Together, this study demonstrated that C. parvum infection results in significant changes in host biochemical pathways and provides new insights into specific biological processes of infectious disease caused by an intracellular protozoan parasite.

Cryptosporidium parvum genes containing thrombospondin type 1 domains.

Cryptosporidium parvum is recognized as an enteropathogen of great worldwide medical and veterinary importance, yet understanding of its pathogenesis has been hampered in part by limited knowledge of the invasion machinery of this parasite. Recently, genes containing thrombospondin type 1 (TSP1) domains have been identified in several genera of apicomplexans, including thrombospondin-related adhesive proteins (TRAPs) that have been implicated as key molecules for parasite motility and adhesion onto host cell surfaces. Previously, a large-scale random survey of the C. parvum genome conducted in our laboratory revealed the presence of multiple genomic DNA sequences with a high degree of similarity to known apicomplexan TRAP genes. In the present study, TBLASTN screening of available C. parvum genomic sequences by using TSP1 domains as queries identified a total of 12 genes possessing TSP1-like domains. All genes have putative signal peptide sequences, one or more TSP1-like domains, plus additional extracellular protein modules such as Kringle, epidermal growth factor, and Apple domains. Two genes, putative paralogs CpTSP8 and CpTSP9, contain predicted introns near their amino termini, which were verified by comparing PCR products from cDNA versus genomic DNA templates. Reverse transcription-PCR analysis of transcript levels reveals that C. parvum TSP genes were developmentally regulated with distinct patterns of expression during in vitro infection. TRAPC1, CpTSP3, and CpTSP11 were expressed at high levels during both early and late stages of infection, whereas CpTSP2, CpTSP5, CpTSP6, CpTSP8, and CpTSP9 were maximally expressed during the late stages of infection. Only CpTSP4 was highly expressed solely at an early stage of infection.