I have been dissecting chick embryos this whole week for the primary culture of their fibroblasts, dorsal root / spinal ganglion (cluster of nerve cell bodies), and cardiac cells. In these fluorescence microscopy images, the fibroblasts appear to have an elongated, triangular, heterogenous morphology while the ganglion have a shiny ring around their cell body with thin long protrusions which are the neurites (axons or dendrites).
In Dr. Mason’s words, “DRG cells are special. Process that goes to skin is dendritic and the one to CNS is an axon. But both look like axons.” That is, DRGs are pseudounipolar cells – they have two axons instead of having an axon and dendrite. One axon extends centrally toward the spinal cord; the other axon extends toward the skin or muscle.
The beauty of our immune system lies in the diversity of the cells involved in the responses triggered by a range of pathogens. These responses can be broadly classified into two groups: innate immune response, which is mainly a non-specific first line of defence, and adaptive immune response, which is acquired over the lifetime of all vertebrates and contains highly differentiated cells that are specific to the antigen. These cells are capable of recognizing the antigens upon secondary exposure and therefore contribute to the memory of the immune system.
Until now, natural killer (NK) cells were considered to be a significant part of the innate immune system participating in non-specific responses. These cells play important functional roles against tumor cells and virus infected cells, through their cytolytic activity. Like T and B cells of the adaptive immunity, NK cells do not express RAG (recombination-activating gene) proteins that are required for assembling the antigen specific receptors on the cells. Based on this concept, RAG knockout mice are common model organism to study cell-mediated immune responses as they lack a functional adaptive system.
Contact hypersensitivity (CHS) is another significant experimental model used to study cell-mediated immune function in the context of memory.1 In this, epidermal cells that are exposed to haptens (compounds that modifies proteins and elicit an immune response) exhibit a delayed-type hypersensitivity reaction. It was first shown by O’Leary et al.2 that Rag2 knockout mice exhibited hapten induced CHS due to NK cells, thus confirming the role of NK cells in memory responses.
So how did O’Leary et al. confirm that it was indeed NK cells that was responsible for inducing hypersensitivity and not other cell types of the innate immune system? As shown in Fig. 2 above, Rag2 knockout mouse that is incapable of producing mature T and B cells still reacted to the hapten. However, Rag2/II2rg double knockout mice did not exhibit the hypersensitivity reaction when exposed to haptens. These double knockout mice lack NK cells along with T and B cells. Moreover, the Rag2 deficient mice that were treated with anti-NK 1.1 antibody (binds to receptors on NK cells and prevents activity) also showed no hypersensitivity response to the haptens. The wild type mice treated with anti-NK 1.1 antibody exhibited CHS due to the activity of T and B cells.
The study of immune responses is still a new and exciting field with many unanswered questions and unknown terrains yet to be discovered. This novel insight on NK cells possessing adaptive immune-like responses and its role in memory could be significant in designing next generation vaccines against a range of pathogens.
Gaspari AA, Katz SI. Contact hypersensitivity. Current Protocols in Immunology. 2001 Chapter 4, Unit 4 2.
O’Leary, J.G. , Goodarzi, M. , Drayton, D.L. & von Andrian, U.H. T cell- and B cell- independent adaptive immunity mediated by natural killer cells. Nature Immunology.7, 507–516 (2006).
Earlier this month, the CDC officially announced the first confirmed case of MERS coronavirus in the United States. Interestingly, the virus was identified in a man who flew from Saudi Arabia to Chicago, and then traveled to Indiana – where he reported symptoms such as fever and cough at a Community Hospital in Munster, Indiana – not very far from where I stay. I have taken one of these buses to get to the airport in Chicago many times before. After having written about the transmission of the virus a few months back, and after having diligently kept track of its spread across the globe, I was amused when it ended up a few miles away from me (of all places!).
Another coincidence is that I was asked about the scientific accuracy of the transmission of MERS-CoV along the lines of the movie Contagion – in which a single infection of Nipah virus leads to a pandemic within weeks. Interestingly, Nathan Wolfe (about whom I wrote previously) was the ‘virus advisor’/consultant for the movie!
These are some really unusual coincidences that interconnected with my flow of thoughts and makes things very interesting while following up with the news from the world of popular science.
Up until now, discovering new viruses was limited to recognizing the symptoms caused by their infections in humans and other animals. Dr. Nathan Wolfe and his team of researchers have reinvented the process of hunting down new, unknown, deadly viruses before they spillover to other animal hosts, including humans. Along with the native hunters, these scientists walk through the deep jungles of central Africa (home to the majority of emerging viruses and reservoir animals), collecting blood samples from primates, snakes, rodents (bush meat for the natives) in order to identify the unknown pathogens.
According to recent statistics, about 75% of the newly emerging diseases are zoonotic (i.e., of animal origin), out of which are a majority of human viruses like Rabies, SARS, Ebola, HIV, Influenza. This calls for a review of our previous and current system of identification and prevention of new pathogens. This process requires collaborators to head to the source, undertake the legwork, and prep the region locals by educating them about the risks and dangers involved in their day-to-day encounters with deadly viruses.
I was introduced to Nathan Wolfe’s work in my Virology class last semester and his TED talk remains to be one of the most inspiring (and one of my favorite) talks. It struck a chord in the sense that it made me realize that biological science research isn’t limited to working in the laboratory, and sometimes involves getting out there in the field to change the course of actions. In Dr. Wolfe’s words, “We may have charted all the continents on the planet, and we may have discovered all the mammals, but that doesn’t mean that there’s nothing left to explore on Earth.“
Humans have been modifying plants for thousands of years. Selective breeding or artificial selection techniques to improve plant quality have evolved into powerful tools for producing a large variety of plants. The biotechnology industry has developed newer techniques of genetic modification over the last twenty years. Genetically modified plants with specific traits can be created with great accuracy in a short amount of time compared to the conventional plant breeding methods that can often be inaccurate and time consuming. The European Commission in 2001 defined genetically modified organisms (GMOs) as “organisms in which the genetic material has been altered in a way that does not occur naturally by mating and/or natural recombination1.”
How are GM crops produced?
Genetic modification involves the introduction of a “gene of interest,” also called the “trans-gene” from another organism, usually bacteria, into the target plant in which a new trait is desired. These new traits could be: extending the life of the plant, making the plant resistant to pest attacks, tolerance to chemicals, slowing down natural decay, improving nutrient content, etcetera. Promoter and terminator genes that can switch on and off the gene of interest are introduced into the plant through the vector, along with a marker gene that signals the modification or transformation of cells.
The latest and most commonly used method is the biolistic method (also known as the gene-gun method). The gene gun injects cells with genetic information using a heavy metal element bullet, like tungsten, coated with plasmid DNA. The gene gun can be used on any type of cell and is not limited to transforming genomes in the nuclei. This process is highly uncertain in the sense that the gene may be introduced in an undesirable location within the plant genome which may result in adverse effects. Also, multiple copies of the gene may be inserted, fragments of genes from the vector may get associated with the trans-gene, and mainly, transformation-induced mutations like rearrangement, deletion and replication of the plants own genes are sometimes observed.
In the vector method, the gene of interest is introduced directly into the plant genome through viral vectors. When the virus integrates into the plant genome as a part of its natural replication cycle, it takes with it the newly engineered portion that expresses the required protein that induces a new trait in the plant. Another method involves using the bacterium, Agrobacterium tumifaciens, as the vector for the DNA. Agrobacterium is widely used to modify sugar beet, oilseed rape, maize and rice plants. Like viruses, it has the ability to insert DNA directly into the plant genome.
The plasmid method involves inserting the gene of interest into a plasmid – a small DNA molecule that is capable of independent replication in a bacterial cell. This is done by cutting open the plasmid DNA by using certain restriction enzymes and introducing the DNA sequence of the required trait. This plasmid DNA with the new additional sequence is then introduced into a culture of live bacteria, which starts to express the desired proteins.
Scientific, Social and Ethical Issues
As mentioned before, there is a high degree of uncertainty and inaccuracy in the techniques used to genetically modify organisms. One cannot disregard the implications of the genetic modification processes after having studied the molecular aspects of gene positioning and gene silencing techniques. The science of GM crops is still at a comparatively early stage, as the detailed function and significance of most plant genes are still unknown. It is quite certain that GM crops need to be grown, consumed and analysed for a long period of time in order to draw scientific conclusions about their safety.
Some of the main issues of concern for human health include – the possibility of allergenicity, gene transfer and outcrossing. An allergenic protein may be induced during modification of the plant. The Food and Agricultural Organisation of the UN (FAO) and WHO test for allergenicity caused due to GM foods. So far, no cases of allergenicity caused due to GM foods have been reported. Since the effect of GM foods on human health is not adequately understood, concern arises about the use of bacterial or viral DNA during the process and the intake of trans-genes by our body. Outcrossing may occur when the genes from the GM crops moves into conventional crops resulting in an indirect effect on food safety and food security. Proponents of GMOs argue that gene flow occurs widely throughout nature, and the risks of such phenomena should be assessed on a case-by-case basis.
This calls for serious active participation from the scientific community in public policy decision making and contribute their understanding of the possible implications of GM foods during worldwide discussions. Integrity and ethics in research is the forefront of any scientific advancement. The GMO debate today finds itself to be in-between crossfires of scientists claiming both the dangers and benefits of GM crops. One can genuinely question the integrity of scientific research that is grounded in public good, when large corporations influence it.
Another issue of GM foods has to do with the corporate control of the food supply. The majority of the agricultural biotechnology corporations like Monsanto, Syngenta, Calgene and BASF control most of the technology used to create GM crops, including agrochemicals and seeds/tissues needed to grow new plants. These companies, along with those who hold the intellectual property rights, have an influence over the availability and use of GM crops. Advancements in the field to produce safer options to the people require access to this technology. Also, it has been known that most of GM research today only serves large-scale farmers in developed countries. A greater expansion in the field is required so that small-scale farmers in the developing countries also benefit from the technology. Much of the opposition related to this comes from the fact that farmers from the poorer countries will then have to depend on the large corporations to acquire seeds every year as opposed to conventional agriculture, where a part of the seeds produced in one growth year are reserved for the upcoming year.
Labelling of GM foods is another controversial issue. Those in favour of labelling of GM foods believe that it is the consumers’ right to know what’s in their food, especially if health and environmental concerns about some foods have been raised. Some people want to avoid eating animal products (including animal DNA) due to ethical and religious reasons. Opponents of labelling argue that with respect to health effects, there have been no significant differences between GM foods and conventional foods. If allergenicity were detected, the food product would have had the current FDA labelling for that allergenic effect. Other aspects of the labelling controversy deal with expenses and non-available infrastructure (storage, processing, and transportation) of the food industry to segregate GM and non-GM foods2.
Potential benefits and conclusions
GM crops have a considerable potential for improving agriculture, and solve many of the world’s hunger and malnutrition problems. GM crops can help preserve the environment by reducing dependence on herbicides and pesticides. Genetic Engineering technology is our future and cannot be ignored due to its enormous potential benefits. The possible risks and benefits associated with the technology can only be assessed on a case-by-case basis.
An EU funded study looking at the safety of GMOs concluded: “There is, as of today, no scientific evidence associating GMOs with higher risks for the environment or for food and feed safety than conventional plants and organisms3.” The U.S. National Academy of Sciences similarly states: “To date, no adverse health effects attributed to genetic engineering have been documented in the human population4.” Yet there are many challenges that governments of the nations have to face with respect to international policymaking, level of regulation, labelling, risk assessments, liability and safety testing.
We have an ethical obligation to explore the potential of GM crops responsibly and be actively involved in influencing governments during policy making. We must proceed with caution and avoid any unintended harm towards the environment and human health in the process of exploring this powerful technology.
Directive 2001/18/EC of the European Parliament and the Council of 12 March 2001 on the deliberate release into the environment of genetically modified organisms and repealing Council Directive 90/220/EEC, Official Journal of the European Communities, L106 (2001)
The Scientific American: “GMO Labelling Debate Follow-up” by Kevin Bonham. (Nov 11, 2013)
European Commission – IP/10/1688: Compendium of results of EU-funded research on genetically modified crops. (2010)
National Academy of Sciences. Safety of Genetically Engineered Foods: Approaches to Assessing Unintended Health Effects (2004)