Sunday, January 19, 2014

New method of vaccine delivery?

Researchers take advantage of immune cells in the skin and solve some major roadblocks to vaccine delivery. Could this be applied to the mucosa? Could this replace the needle and syringe?

Tony Song

Monday, December 23, 2013

The Link Between Autoimmunity and Infectious Disease

Autoimmunity occurs when the immune system begins to wrongly attack self-antigens or various parts of the body it’s responsible for protecting. There are mechanisms in place to prevent this kind of problem, while still allowing B and T-cells the variability needed to combat a wide array of pathogens (disease causing agents). Mechanisms are in place during the production of B and T-cells that check them for auto reactivity, such as central and peripheral tolerance. The breakdown of these tolerance mechanisms causes autoimmunity. When central tolerance mechanisms breakdown, auto reactive B-cells escape negative selection, in the form of apoptosis (cell death), and are released into the lymphatic system. It is when these auto reactive B-cells become aberrantly activated through things like B and T-cell discordance or T-cell bypass that an attack on host tissues begins.
            Some autoimmune diseases are caused by the production of autoantibodies against self-molecules, which are produced when auto reactive B and T-cells escape tolerance mechanisms. The production of autoantibodies against key components in the immune system, like inflammatory cytokines (signaling molecules) can negatively affect the ability of the immune system to effectively clear pathogens and prevent disease. In other words, autoimmunity can predispose people to infection by various pathogens, which they would normally be able to eradicate if their immune system was uncompromised.
            One of the most vital aspects of the immune system is the ability of the various immune cells to effectively communicate with one another and influence the environment around them. This is done through the use of signaling molecules known as cytokines. They are a diverse group of soluble proteins, peptides or glycoproteins that are secreted by specific immune cells in order to elicit a specific response. Therefore many times when an infection is detected inflammatory cytokines such as TNF-α are released, which induces things like vasodilation. Thus, by increasing the amount of immune cells flowing to the site of infection the environment around the pathogen is effectively skewed to favor the immune system. Cytokines can also act as effector molecules to polarize T-cell responses in order to rid the body of the pathogen in the safest and most effective way possible. For instance, if an extracellular pathogen like Streptococcus (the bacteria that causes strep throat) began to infect your nasal system you would want a Th2 (antibody mediated) response to be deployed as opposed to a Th1 (CTL mediated) response. A Th2 response is much safer and more effective against extracellular pathogens because, unlike a Th1 response, a Th2 antibody-mediated response doesn’t involve the release of cytotoxic granules or pro-inflammatory molecules, which could really damage these sensitive tissues. In order for a T-cell response to be skewed towards a Th2 response the cytokine IL-4 must be present and continue to remain in the environment. So, if a person suffered from an autoimmune disease, which produced autoantibodies against IL-4 they would be unable to effectively combat extracellular pathogens like Streptococcus, and in a sense they would be classified as immune compromised.

Sunday, December 22, 2013

SCARF1: A Novel Receptor for Apoptotic Clearance

            Autoimmunity is one of the most difficult to treat and unfathomable types of disease, because we are not fighting a virus, bacterium, or parasite: we are fighting our own body. Usually, doctors can count on the immune system to help them out when their patients are sick; it is the job of this system to ensure that any foreign threat to the body is eliminated. But the nature of autoimmunity is such that the biggest ally we have in the quest to keep ourselves healthy turns against us and begins attacking that which it has evolved to protect.
There are many classes of autoimmune disease, each with a very different cause. The immune system is so diverse and complicated that a mutation in one of its parts can affect the entire system and ultimately manifest in disease. There are myriad ways in which this can happen, but the result is what is called “breaking tolerance”. When tolerance is broken, the immune system recognizes some small component of the body as a foreign object and mounts an immune response against it. This can cause differing amounts of damage, depending on how prevalent the component is, and if its recognition and destruction leads to the labeling of more self proteins as targets. There is the danger of a phenomenon called epitope spreading, which happens when a cell is targeted and destroyed, releasing its contents into the body. The immune system has not been desensitized, or “tolerized” to the proteins inside a cell, as it should have no need to recognize them in a healthy body. When this happens in the context of an already active self-targeted immune response, immune cells may further target the otherwise normal contents of the dying cells, leading to a more serious attack throughout the body.
            One important safeguard against autoimmunity is the safe breakdown clearance of apoptotic cells. An apoptotic cell is one that is infected, compromised, or simply too old and losing effective function. These cells are marked for uptake by phagocytes, which are a class of cell types that uptake and destroy their targets, breaking down anything in the cell that could be toxic if released into the body. It is known how and when phagocytes such as macrophages and dendritic cells destroy their targets, but the specifics of their identification are little investigated. In their paper “The scavenger receptor SCARF1 mediates the clearance of apoptotic cells and prevents autoimmunity”, Zaida G. Ramirez-Ortiz et al identify and characterize the receptor SCARF1 which, allows phagocytes to recognize their targets for destruction. SCARF1 is a transmembrane protein which has homologs even in the simple research model C. elegans, and acts by binding to a C1q and phosphatidylserine complex. Phosphatidylserine is a part of the inside of the cell membrane, and becomes exposed on the exterior portion of the membrane only when the cell needs to be phagocytosed. SCARF1, the researchers found, cannot recognize and destroy cells without this component bound to C1q, a peptide which also plays a role in the complement system. High concentrations of this peptide near a cell marked with phosphatidylserine cause a complex to form, which binds to SCARF1 and results in successful phagocytosis. 
Cover image expansion
1. Macrophage Engulfing Apoptotic Cells

Friday, December 20, 2013

A New Vaccine to Protect Against Malaria

Malaria mosquito (4)
Malaria protozoan (5)
A New Vaccine to Protect 
Against Malaria

Malaria cases by country (6)
Malaria is a serious mosquito-borne illness that is present in tropical and sub-tropical countries all over the world. Roughly 3.3 billion people, almost half of the world’s population, live in areas where malaria is endemic (1). Malaria is caused by a unicellular eukaryotic organism called a protozoan. The protozoan that causes malaria, Plasmodium falciparum (Pf), replicates in human liver and red blood cells causing these cells to die. Uninfected mosquitos can then pick up the sporozoite by biting an infected person, thus propagating infection. Malaria causes high fevers, chills, and other flu-like symptoms, and can sometimes result in death (1).

Life cycle of plasmodium falciparum (7)
The protozoan that causes malaria is transmitted by mosquito bite as a sporozoite, an infectious form of the protozoan that is produced by asexual reproduction. Plasmodium falciparum lives in a mosquito’s mouth in the saliva, and when a human gets bitten, the sporozoites are transmitted to the human where they first replicate asexually in the liver and then spread to the blood and cause serious disease (1). In recent years many control interventions have been developed to attempt to reduce the number of cases of malaria; these include using bednets sprayed with insecticide in areas where malaria is endemic, spraying insecticides, and administering antimalarial drugs. Despite these efforts, in 2010 alone there were 220 million reported malaria cases, causing somewhere between 0.66 and 220 million deaths, the majority of those infections occurring in young children. Thus the current preventative measures are not sufficient; a vaccine against malaria will be the best method to combat malaria infections (2).

The most effective vaccine will be one that targets the sporozoite while humans are still asymptomatic; this is when the sporozoite has not yet spread from the liver to the blood (3). The World Health Organization has set a goal of obtaining a vaccine that is 80% effective by 2025. However, despite years of research and development, no current vaccines reach this level of efficacy. Currently the only way to confer protective immunity against malaria is by injecting people with inactivated sporozoites from >1000 mosquitos (the inactivation of the sporozoite is done by irradiation). Clearly, breeding this many mosquitos and isolating sporozoites from each one is not an optimal means of vaccination. As a result, a research group developed a way to grow radiation-attenuated Pf sporozoites (PfSPZ). The researchers attempted to vaccinate people subcutaneously, under the skin, but this method only caused minimal immune response and very low protective immunity. Recently however, the same group of researchers found that injecting PfSPZ intravenously (IV) provides protective immunity against malaria.  

The recent study used a vaccine with various doses of PfSPZ and injected it intravenously multiple times over the course of several weeks. The study participants, termed vacinees, were infected with controlled human malarial infection (CHMI), which involves giving a low dose of sporozoites and intervening with anti-malarial medications as soon as patients become symptomatic.  There were three study groups, with control individuals in each group whom did not receive the vaccine but were infected with CHMI. The three groups of vacinees received three different doses of PfSPZ, and varied in the number of vaccines of each dose administered. While protection was low in the group receiving the lowest dose, there was significant protection against malaria infection in the group receiving the highest dose of PfSPZ. In the group that received the highest concentration of PfSPZ per dose, 1.35 X 105, and were administered the vaccine four or five times provided 66% and 100% protection against CHMI respectively. These results were promising, so the researchers then looked to see what types of immune responses were being elicited that were providing protection against CHMI.

Combined Immunotherapy as a means of stopping prolonged treatment with ART?

The HIV-1 virus has evolved to exploit the human immune system and counteract all immune defenses mounted against it.  Many different vaccination approaches and therapy treatments have been attempted to control, eliminate, or prevent HIV-1 infection, however, these attempts have not proved successful for virus elimination from the body. 
One approach that has been used to combat HIV-1 infection is the use of ART, or antiretroviral therapy, and this approach has proven to be effective at reducing viral levels in the blood.  ART suppresses HIV-1 viremia to undetectable levels within 12-48 weeks in a majority of patients.  This therapy is a “cocktail” or combination therapy of three or more drugs, including 2  nucleoside-based reverse transcriptase inhibitors (prevents production of the virus genome by inhibiting RNAàDNA transcription), and one or more of the following drugs: non-nucleoside reverse transcriptase inhibitors, membrane fusion inhibitors, viral protease inhibitors, or integrase inhibitors.  Each of these drugs targets a specific part of the viral lifecycle, making it unable to replicate and infect other cells.  Because each drug is mutually exclusive and targets a different area of the lifecycle, it is unlikely that a virus will develop resistance to all three drugs.  Therefore, because the virus does not produce escape mutants from the therapy, this approach is effective at reducing viral levels in the blood (ART information) (more on ART) However, by the time ART is put into effect, the virus has already established residence in T cells in the body, and can continue to infect other cells undetected by the drug by avoiding exposure in the blood via direct cell-to-cell infection.  Another problem with the use of ART for HIV-1 treatment is that it must be administered indefinitely, and if it is discontinued, there is a rapid rebound of viremia, or viral infection of the blood.  Taking ART indefinitely is undesired due to negative side effects (common ART side effects) and resistance to the drugs that develops overtime due to mutation.
Another approach to combat HIV-1 infection has been the use of monoclonal neutralizing anti-HIV-1 antibodies, however, in the past, these antibodies have proven to be ineffective at controlling infection of humanized mice (hu-mice) (Hu-mice as the murine model for the analysis of human hematolymphoid differentiation and function).  However, as of late, more potent antibodies have been uncovered that have decreased viremia in hu-mice and have longer half lives.  Antibodies that target gp120 glycoprotein in the HIV viral envelope have been studied as a potential means of neutralizing HIV infection.  Gp120 binds to CD4 on T cells, enabling initial viral-cell contact before membrane fusion and insertion of the viral genome (more on gp120). 
In a recent study conducted by Horwitz et al (2013) (published in the Proceedings of the National Academy of Sciences of the USA: HIV-1 Suppression and durable control by combining single broadling neutralizing antibodies (bNAbs) and antiretroviral drugs in humanized mice), three antibodies targeting different epitopes of gp120 were used in combination with ART and the effects were analyzed.  The three antibdies were 3BNC117 (a potent CD4 binding site antibody with a long half life), PG16 (which recognizes the V1/V2 loop region), and 10-1074 (which targets the base of the V3 stem). 

Identifying the Unknown Contributors to Shellfish Allergies

According to a 2004 study in the Journal of Allergy and Clinical Immunology, seafood allergies are reportedly present in 2.3% of the general population, or approximately 6.6 million Americans (Sicherer, Munoz-Furlong, and Sampson, 2004).  This represents a serious health concern for the U.S.  With seafood – notably shellfish – consumption having risen in popularity and frequency globally, it has become pertinent that shellfish allergies become better characterized (NOAA, 2013).
     The manifestation of shellfish allergies can be highly variable with symptoms ranging from hives, tingling or swelling of the lips, tongue or throat, chest tightness, shortness of breath or difficulty breathing, nausea and vomiting, to full-blown anaphylaxis (Cleveland Clinic,2012). The allergens associated with shellfish allergies are not well characterized and thus management of such an allergy is often simply limited to avoidance or dietary elimination of shellfish.   Additionally, treatment is restricted to emergency care following exposure (Lieberman et al.,2010). So far, it is known that there are heat stable antigens within shellfish that bind to human IgE, an immunoglobulin or antibody that likely originally evolved as a defense against internal parasites such as helminthes and now significantly contributes to immune-mediated hypersensitivity reactions. Once bound to an allergen, IgE initiates intracellular signaling, leading to the degranulation of immune cells. Degranulation is the release of antimicrobial cytotoxic molecules and mediators of inflammation, which in this case eventually leads to the previously described symptoms. One major type of shrimp allergen that has been identified is tropomyosin, a protein associated with the thin filaments in muscle cells and microfilaments in non-muscle cells. However, there are many other IgE reactive shellfish proteins that have yet to be identified
     A recent study published in PLOS One sought to identify and study different IgE-reactive components of commonly eaten shellfish.  The investigators primarily sought to compare the IgE reactivity of raw and heated proteins of the blue swimmer crab and the black tiger prawn. By treating whole blood and blood sera of individuals with and without shellfish allergies with raw and cooked shellfish extracts, investigators were able to quantifiably measure the degree to which IgE reactivity occurred in response to treatment and to identify unique IgE reactive proteins.