Cryptosporidium, the understudied killer

Diarrhea is the second major killer of children under the age of 5 in developing countries (second to pneumonia). We know much less than we should about the causative agents, severity, burden etc. of diarrhea in developing countries. Funded by Bill and Melinda Gates Foundation, A Global Enteric Multicenter Study (GEMS) picked up the task of learning more about diarrhea in children in developing countries with high incidence (Gambia, Mali, Mozambique, Kenya, India, Bangladesh and Pakistan)   and did an extensive 3 year-long case-control study. I won’t go to details about their magnificent work but just mention one rather surprising finding. They found the 4 top pathogens causing diarrhea in children under 5 to be: 1. Rotavirus 2. Cryptosporidium 3. Shigella 4. Enterotoxigenic Escherichia coli producing heat-stable toxin (ST-ETEC). Rotavirus has long been known as a major cause of diarrhea in children and there are effective vaccines against it who have significantly reduced its incidence in developed countries. Shigella and ST-ETEC were also previously known. But the high incidence of Cryptosporidium has come out as a surprise to everyone. Crypto is an apicomplexan protozoan parasite, kin to other famous parasites Plasmodium and Toxoplasma. It’s durable cysts are shed in the stool and can be ingested in contaminated food and water. Compared to the other top pathogens and with regards to the high mortality it is causing, Crypto is relatively unpopular and extremely understudied (even reflected in its Wikipedia page). Now GEMS calls for more research on Crypto and better therapies against it. Hopefully this would mean more funding for studying this bizarre parasite and more exciting knowledge learnt from its biology and pathophysiology. 

Find and share GEMS infographic about their findings from here.

Cryptosporidium trophozoite bound to the small intestine epithelium, inducing actin accumulation at its binding site

Cryptosporidium trophozoite bound to the small intestine epithelium, inducing actin accumulation at its binding site. From Elliott and Clarck, Infection and Immunity, 2000

Kotloff, K., Nataro, J., Blackwelder, W., Nasrin, D., Farag, T., Panchalingam, S., Wu, Y., Sow, S., Sur, D., Breiman, R., Faruque, A., Zaidi, A., Saha, D., Alonso, P., Tamboura, B., Sanogo, D., Onwuchekwa, U., Manna, B., Ramamurthy, T., Kanungo, S., Ochieng, J., Omore, R., Oundo, J., Hossain, A., Das, S., Ahmed, S., Qureshi, S., Quadri, F., Adegbola, R., Antonio, M., Hossain, M., Akinsola, A., Mandomando, I., Nhampossa, T., Acácio, S., Biswas, K., O’Reilly, C., Mintz, E., Berkeley, L., Muhsen, K., Sommerfelt, H., Robins-Browne, R., & Levine, M. (2013). Burden and aetiology of diarrhoeal disease in infants and young children in developing countries (the Global Enteric Multicenter Study, GEMS): a prospective, case-control study The Lancet DOI: 10.1016/S0140-6736(13)60844-2

Elliott, D., & Clark, D. (2000). Cryptosporidium parvum Induces Host Cell Actin Accumulation at the Host-Parasite Interface Infection and Immunity, 68 (4), 2315-2322 DOI: 10.1128/IAI.68.4.2315-2322.2000
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A systematic review in non-clinical research: a case of pathogen metabolites

Posted by Kasra

Doctors and scientists in the field of clinical research are well acquainted to systematic reviews and their importance in clinical research. The important difference between a normal review and a systematic review is that in the latter the authors make sure (or at least try very hard) to include and cover all the published research about the topic of review. Along with the review of the data, they should also publish the search strategy they used to make sure they get everything that has been published about their topic of study. Collecting all the data is extremely important especially when deciding about the beneficial effects of a certain drug, vaccine or public health intervention.  The Cochrane collaboration is a well-known organisation that collects and publishes systematic reviews in field of health research and health care.

Although they could be very useful in non-clinical research, systematic reviews are actually rarely written in these fields. During my graduate studies, I had to write a systematic review on innate receptors for a certain fungus. I realized then how diverse the experimental models are and how hard it is compare their controversial results due to small or big differences in experimental setup and strains used. Maybe that is why these papers are rare in non-clinical research. Still, no matter how hard, I was able to do it with as much time as a graduate student would put on a term paper and get a good grade for it ;). I am looking forward to reading more non-clinical systematic reviews.

Recent work of Bos et al. is an excellent example of how useful it could be to gather all the available data in a certain field, even if it is not all clinical trials. They point to most common abundant bacteria in sepsis Staphylococcus aureus (SA), Streptococcus pneumoniae (SP), Enterococcus faecalis (EF), Pseudomonas aeruginosa (PA), Klebsiella pneumoniae (KP), and Escherichia coli (EC). They argue that current strain detection methods are too slow and do not allow for efficient targeted antibiotic therapy. On the other hand, non-targeted therapy is not always successful. They argue that the unique and some-what well-identified metabolic pathways of these bacteria leads to production of certain volatile chemicals that are not produced by humans and could be used as rapid diagnostic markers. The diagram below shows the gram positive bacteria on the left and gram negative bacteria on the right, graphing unique and common volatile chemicals they produce. The blue circle in the center shows the chemicals produced by all bacteria. Therefore, their absence would exclude infection. The red (or pink as you may) circles highlight the unique products of each species which could help in targeted antibiotic therapy of sepsis.

Staphylococcus aureus (SA), Streptococcus pneumoniae (SP), Enterococcus faecalis (EF), Pseudomonas aeruginosa (PA), Klebsiella pneumoniae (KP), and Escherichia coli (EC)

Bos, L., Sterk, P., & Schultz, M. (2013). Volatile Metabolites of Pathogens: A Systematic Review PLoS Pathogens, 9 (5) DOI: 10.1371/journal.ppat.1003311

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Detecting picograms of protein in the secretome

Posted by Kasra

When designing experiments in the lab, we usually say we cannot check for everything. Well, what if we could?! Meissner et al. used only 150,000 macrophages per sample to analyze their secretome. They have been able to detect and quantify protein abundances at the picogram level in a label-free system. Picogram detection limit means that cytokines are readily quantifiable, and Meisner et al. claim it matches with the detection limit of ELISA. I could imagine that in not so long this technology can become more readily accessible, allowing researchers to acquire more pertinent data per sample. We can know the statuses of a multitude of proteins (from cytokines to nonconventionally secreted proteins) simultaneously, not through multiple ELISAs and western blots, and therefore draw much more sensible conclusions from experiments. It will actually be more affordable than separate quantification of each protein, not mentioning dramatically time-saving.

Also, this data can be integrated with other high throughput quantitative analyses of the cell. For instance, Meissner et al. have compared the changes in protein abundance in the secretome to changes in their transcript levels, and roles of different adaptor molecules (in this case MyD88 versus TRIF) and tried to explain how they all relate.

Meissner F, Scheltema RA, Mollenkopf HJ, & Mann M (2013). Direct proteomic quantification of the secretome of activated immune cells. Science (New York, N.Y.), 340 (6131), 475-8 PMID: 23620052

ResearchBlogging.org

An intracellular receptor for antibodies

Posted by: Kasra

We usually consider exiting the phagolysosome and entering the cell cytoplasm to be a immune evasion mechanism for pathogens. The pathogens inside the phagolysosome can be processed and presented via MHCII to the adaptive immune system, but once free of that compartment, the pathogen could potentially ‘hide’ from the immune system, well apparently not that much! Apart from the intracellular pattern recognition receptors (NLRs), researchers have found another receptor that responds to intracellular presence of antibodies. McEwan et al. showed that if antibody coated viruses or bacteria have entered the cytosol, presence of the Fc part of the antibody can be sensed by a protein called TRIM21. This could in turn result in an inflammatory and anti-viral response by activating NF-κB and AP-1 and production of cytokines. To me, this is an excellent example that shows how the host and the pathogens have evolved together for many years becoming more and more complex through an arms race.  A newly developed strategy by one party is followed by a counter strategy by the other party.

NatImm

From Geijtenbeek TB, & Gringhuis SI (2013). An inside job for antibodies: tagging pathogens for intracellular sensing. Nature immunology, 14 (4), 309-11 PMID: 23507635

McEwan WA, Tam JC, Watkinson RE, Bidgood SR, Mallery DL, & James LC (2013). Intracellular antibody-bound pathogens stimulate immune signaling via the Fc receptor TRIM21. Nature immunology, 14 (4), 327-36 PMID: 23455675

Geijtenbeek TB, & Gringhuis SI (2013). An inside job for antibodies: tagging pathogens for intracellular sensing. Nature immunology, 14 (4), 309-11 PMID: 23507635

ResearchBlogging.org