The Nature and Effect of Superbug H1N1 - Coursework Example

INTRODUCTION Influenza is an infection caused by a virus of the same that, in humans, preferentially attaches and cause harm on the lungs. Its symptoms include fever, cough and severe muscle aches. The infecting agent and symptoms should naturally wane within a few days, although they still have caused death among the elderly and immunocompromised individuals because the disease makes the infected person more susceptible to bacterial infection. In fact, it has caused several plagues, claiming the lives of as much as 20-50 million people worldwide (Kimball, 2009). Despite these devastating effects, it took 15 years for researchers to determine the causative agent of Influenza disease. The Influenza virus is a 100 mm vessel containing matrix proteins and 8 strands of RNA, and enclosed by a lipid bilayer studded with membrane proteins hemagluttinin (HA) and neuraminidase (NA). HA molecules are particularly important in the development of the disease as they cause the preferential attachment to lung epithelial cells and the insertion of the virus contents into the host cell. Each protein in the virus has multiple subtypes. In human-infecting Influenza virus strains, there are three HA subtypes, H1, H2 and H3, while NA has two, N1 and N2. The different combinations of HA and NA make possible the multiple subtypes of Influenza viruses (Kimball, 2009). With the elucidation of the viral structure, it has since been discovered that there are multiple strains of the virus, and that they continually mutate and cross-infect swine, birds and humans. As commonly seen among viruses, HA, together with NA, genes mutate at a high rate, causing new strains to be seen infecting humans almost yearly. This phenomenon is referred to as the antigenic shift. In addition, Influenza virus strains undergo gene reassortment, in which two strains infecting the same bird or swine exchange RNA strands to develop a new virus subtype that the human population has not been exposed before. Thus, this antigenic shift usually causes severe pandemics. For example, the 1957 H2N2 Asian flu pandemic after the 1918 H1N1 Spanish flu pandemic is believed to be caused by the simultaneous infection of a human-infecting subtype and a bird-specific H2N_ resulting to the reassortment of their genes that produced a new bird-specific subtype that can infect humans. In effect, this new H2N2 subtype is something the human population at that time has not been exposed before, causing many to have no immunity against the virus and to be susceptible to infection (Kimball, 2009). Because of the unique features of Influenza virus, current prophylaxis still involves multiple vaccinations, with the composition of multivalent shots varied annually to confer protection against strains guessed to be most infective during the coming season. Thus, prolonging and ensuring the effectiveness has been the focal point of many researches. A promising approach is the development of vaccines that can induce the production of antibodies that are specific against multiple HA subtypes. Throsby and his colleagues (2008) paved the way for such approach when they identified human antibodies that can bind to H1, H2, H5, H6, H8, and H9. They referred to this antibody as CR6261 (Eckiert et al., 2009). CR6261 AGAINST H1N1 AND OTHER SUBTYPES What makes CR6261 different from other antibodies that confer resistance to only one subtype of Influenza? Eckiert et al. (2009) tried to elucidate the 2.2 and 2.6A crystal structure of the antigen-binding portion (Fab) of CR6261, as well as the CR6261 Fab complexed with heterotypic HAs from human 1918 H1N1 pandemic virus and avian H5N1 virus. Although it was not mentioned in the study if there is any purpose in choosing H1 and H5 instead of the other subtypes, the choices probably served the most purpose because H1 has a history in causing a pandemic (1918 H1N1 Spanish flu), and H5 has a likelihood to infect and cause death among humans, who are mostly unexposed to such type of Influenza (Kimball, 2009). However, it is most ideal if the study was able to analyze the binding of CR6261 to H2, H6, H8 and H9 as well. H2 have caused pandemics on multiple occasions, and the other three, although currently found in birds (H6 and H8) and swine (H9), have the possibility of infecting humans in the future. They then compared these structures to type-specific anti-HA antibodies whose structures were previously elucidated. How did they do it? First, the research team recombinantly expressed the HA and CR6261 Fab molecules through baculovirus and mammalian cells, respectively, both widely accepted expression systems. They have been optimized to produce numerous, easily isolated protein or polypeptide molecules coded by a specific gene, and thus are ideal for purposes of accurately determining the structure of a protein. Then, upon analyzing bound and complexed crystallographic structures at acidic, physiologic and basic pH levels, they found that the binding site of the antibody is at the proximal end of HA, or at the stem of the molecule. The use of different pH is essential as the structure of HA normally modifies upon exposure to pH changes. In addition to structure elucidation, they also determined the activity of CR6261 through agglutination test, which mixes the antibody solution with a mixture of red blood cells (RBC) and HA. If HA causes the RBC to clump together, then the antibody proves to be ineffective in preventing the binding of HA to RBC. What did they find out? The antibody was seen to be specific on the conserved HA2 A helix of the protein, as opposed to the activity of most anti-HA antibodies that bind to the hypervariable region found on the globular head of HA (Fig. 1). This epitope is necessary in the membrane fusion activity of HA, and as was also seen crystallographically, it prevented the pH-induced conformational changes of H1 and H5 that exposes it to trypsin digestion (Fig. 2). In addition, by testing negative for agglutination test (results not shown), the researchers further solidify the evidence that the binding site of CR6261 is different from the usual anti-HA antibodies, which tests positive in agglutination test by causing clumping of erythrocytes. This provides more evidence that CR6261 prevents the membrane fusion activity of HA, which is necessary in exposing the virus genes to the DNA machinery of the host. Why does CR6261 deactivate a wider range of Influenza subtypes? Padlan (2008) suggests that the globular head of HA that attracts most type-specific antibodies undergo a higher rate of mutation, allowing virus strains to mutate and produce new strains that escape the antibodies made upon exposure to other strains and types. In contrast, the stem of HA, to which CR6261 binds to, is made up of amino acid sequence that has remained the same among different strains and types. What is the next step? The findings of Eckiert et al. bring new light in developing more effective Influenza vaccines. By discovering a way to increase the number of CR6261-like antibodies, we become a step closer in providing resistance against a wider range of Influenza. However, the drawback of anti-HA antibodies such as CR6261 is that they are naturally produced less in the body. That is, the globular head that induces the production of type-specific anti-HAs are more immunodominant than the stem. Future studies can thus focus on increasing the amount of CR6261-like antibodies produced during vaccination. One method suggested is de-antigenization, as coined by Padlan (2008), through which a recombinant HA is designed such that the sequence of the globular head is changed to make it have less binding moieties with anti-HA antibodies without modifying so much its original structure. This way, the antibodies that will be made binds to the conserved part of HA already, making it suitable against many types and strains of Influenza virus. However, how to actually increase the number of CR6261-like molecules is still yet to be determined. IMPLICATIONS OF THE STUDY The development of heterotypic vaccines is an important breakthrough in preventing another Influenza pandemic, such as that occurred during the 1918 H1N1 Spanish flu pandemic. However, history in science dictates that it will take a while before these new vaccines are made available for common consumption. But if it happens, the occurrence can be expected to decrease dramatically, since the cost of getting a flu vaccine becomes cheaper (getting one shot for a lifetime instead of a shot per year) and subsequently more people can afford getting immunity. Also, if Padlan’s suggested plan worked out, we might see a new era in large scale vaccine production, in which recombinant technology is used. Instead of using egg-based vaccines that are not only allergenic but wasteful as well, there can be a shift to recombinant vaccine production, in which antigenic molecules are made using cell lines grown in flasks. This will be beneficial to the environment, especially now that the current problem is the excessive pollution the human population is continually excreting. REFERENCES Ekiert, DC, G Bhabha, M Elsliger, RHE Friesen, M Jongeneelen, M Throsby, J Goudsmit, and IA Wilson, ‘Antibody Recognition of a Highly Conserved Virus Epitope’, Science, vol. 324, 2009, pp. 246-251 Kimball, J, The “Flu”, RCN D. C. Metro, 2009, retrieved 6 November 2011, . Padlan, E, ‘De-antigenization of Immunodominant Epitopes: A Strategy for Designing Vaccines Against Constantly Mutating Pathogens and Other Applications’, Philippine Science Letters, vol. 1, no. 1, pp. 9-10 Read More