Measles Pathogen

Identify the specific pathogen/agent, which causes the disease

How is the Human body able to distinguish the pathogen/agent you have studied as “non-self”? If it can’t be identified as “non-self”, why not?

• pathogen responsible for measles is a virus known as paramyxovirus
• Paramyxovirus is generally one of a group of RNA viruses that largely causes acute respiratory diseases and is typically transmitted in an airborne manner
• Measles pathogen is approximately 100 nm to 200 nm in diameter containing an inner nucelocapsid core 18 nm in diameter, comprising of a negative-sense, single-stranded, non-segmented RNA genome.
• The measles pathogen requires only two out of its six structural proteins in pathogenesis and disease progression. These two envelope proteins are; the fusion (F) protein and the hemagglutinin (H) protein.
• The fusion protein is responsible for the fusion of the virus into the host cell membrane, viral penetration, and hemolysis.
• The hemagglutinin protein is responsible for adsorption of virus to cells.

The body’s immune defenses normally coexist peacefully with cells that carry distinctive “self” marker molecules. But when immune defenders encounter foreign cells (viruses like measles) carrying markers that aren’t identical to the ones in the human body, they identify them as “nonself”, and launch an attack.

T cells compare non-self antigens to HLA (human leukocyte antigens) molecules with proteins the system already knows are its own. Your T-cells don't react to your HLA because of tolerance but are not tolerant to the HLA proteins of something else (a virus or another organism). Thus, when there is a non-self system in your body (measles virus), your T-cells will begin a cell-mediated immune response against it, considering them foreign.

Measles Pathogen

Measles Pathogen

By Taylor Giannis

Briefly describe the roles played by both the cellular and humoral parts of the immune system in the defense against the pathogen/agent you have researched.

The third line of defense against pathogenic invasion of measles is the adaptive immune response, which has two key qualities:

• It is specific (it can differentiate between specific microorganisms and respond accordingly)

• It is adaptive (it can produce a heightened response upon re-exposure - has memory)

Humoral immunity involves the resistance to disease by the production of antibodies (immunoglobulin’s) that bind to specific antigens. B cells, which have antibodies, attach to the measle virus antigens floating in the blood. Once this occurs, the antigens will be destroyed via endocytosis and subsequently presented on the surface of the B cell in a MHC class 2 receptor. A T-Helper 2 cell containing the same antibody will bind to the MHC class 2 receptor on the B-cell, This will cause the B-cell to differentiate into plasma cells and memory B-cells. Plasma cells generate free-floating antibodies, memory B-cells stay around in case of later infection.

BIBLIOGRAPHY

Pathogen Profile Dictionary, 2010, The Journal of Undergraduate Biological Studies, accessed 27 April 2014, <http://www.ppdictionary.com/viruses/measles.htm>.

Better Health Channel, 2013, State Government of Victoria, accessed 27 April 2014, <http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Measles>.

The Bodies First Line of Defence, 2014, Science Learning Hub - The University of Waikato, accessed 1 May 2014, <http://www.sciencelearn.org.nz/Contexts/Fighting-Infection/Science-Ideas-and-Concepts/The-body-s-first-line-of-defence>.

Third Line of Defence, 2013, BioNinja, accessed 1 May 2014, http://www.vce.bioninja.com.au/aos-2-detecting-and-respond/defence-against-disease/third-line-of-defence.html.

In the Cell-Mediated response macrophages eat measle pathogens. The antigen is presented on the surface of the macrophage in a MHC class 2 receptor. A T-helper 1 cell with the corresponding antibody on its surface binds to the MHC class 2 receptor containing the antigen. The T-helper 1 cell then activates cytotoxic T cells. Cytotoxic T cells then patrol your body looking for other infected cells. Infected cells will have the antigen presented on the surface of the cell in a MHC class 1 receptor. When the cytotoxic T cell finds an infected cell, it will bind to the MHC class 1 receptor containing the antigen. The cytotoxic T cell will then release Interferon and Tumor Necrosis Factor. The former slows down the infected cell's reproduction, while the latter causes the cell to undergo apoptosis.

The Humoral system takes down pathogens floating in the blood, while the Cell-Mediated response kills cells that have become infected with the pathogen

Briefly outline the two first lines of defense (non-specific) used by the host to defend itself against the pathogen/agent you have researched?

Identify the host/s and/or host cells and state how the pathogen/agent is transmitted form host to host.

The body uses the first and second lines of defense in an attempt to prevent measles. The first line of defense is used by providing a thick impermeable barrier, blocking the entry of bacteria. It is innate and non-specific, using the healthy bacteria on the surface of the body to counteract and compete with any unhealthy bacteria. Examples of the types of 1st line of defense used by the body to counteract measles are; intact skin, mucous membranes, tears, saliva, stomach acidity, blood clotting, and urine. In an aim to defend itself against the entry of the measles pathogen, the body also uses the nonspecific second line of defense. This line of defense goes after any infection with leukocytes (a type of white blood cell).

• Humans are the only species susceptible to the measles virus, and are there the only hosts
• the pathogen is transmitted from host to host by airborne particles such as respiratory droplets coming from nasal or oral cavities of an infected individual
• after gaining entry into its host, it anchors itself to the humans endothelial and respiratory epithelial cells. The H protein of the virus interacts with the F protein to attach and fuse the viral envelope with the host cellular receptors upon attachment. The binding sites on viral H proteins for these receptors overlap and strains of measles virus differ in the efficiency with which each receptor is used.

What are the symptoms caused by the pathogen? How does the pathogen contribute to these symptoms?

Describe any current methods of treating/preventing the disease. Is there a vaccine available?

• coughing
• runny nose
• mildly inflamed conjunctiva (the clear mucous membrane consisting of cells and underlying basement membrane that covers the white part of the eye and lines the inside of the eyelids)
• After these initial symptoms appear a rash that starts approximately three days later.
• Koplik spots, which are small, red, irregularly-shaped spots with blue-white centers also occur on the mucosal surface of the oral cavity.
• The maculopapular rash appears first on the head, and then progressively spreads downward on the hosts body.

• mortality rate: 2 in every 1000 infected patients
• only way to prevent measles infection is through vaccination
• Schwarz vaccine is typically used and is recommended to be administrated to every child at fifteen months of age. The vaccine results in over 95% seroconversion (the development of detectable specific antibodies to microorganisms in the blood serum as a result of infection or immunization) in patients, providing them the ability to fight off infections from this virus, and a booster shot is recommended to ensure lifelong immunity.

The use of the lymphatic system is crucial as it acts as the central location for the distribution of immune system cells. Phagocytes in the form of macrophages (antigen presenting cells) are able to engulf the measle pathogens and carry and present the foreign antigen to other cells of the immune system (T helper cells). Natural killer cells are also used to attack the bodies own cells that have been infected by the measles pathogen. They do this by punching holes in the infected cell walls and injecting chemical that causes apoptosis. The entrance of the measles pathogen into the human body causes signs and symptoms of inflammation such as; redness, warmth, swelling and pain.

The inflammatory response is a localized, nonspecific response to infection causes by the measles pathogen. In order for inflammation to occur histamine is released by the Mast cells and basophil cells, this increases permeability of the capillaries to the white blood cells and some proteins, to allow them to engage pathogens in the infected tissues. Histamine increases blood flow to the site of pathogen to the infected area. Inflammation aids in the prevention of an influx of pathogens by saturating the infected area with heat from the increased blood flow, phagocytes and complement proteins.