Overview
You are a T-helper cell in your immune system and are deciding what parts of the immune system to marshall against an incoming invader. For this assignment, you will be presented with a pathogen and its arsenal of virulence factors that it can use against you. Your job, if you choose to accept it, is to pick the portions of the immune system that you will use against each virulence factor and then describe how that immune system part inactivates the target virulence factor. Here are your potential adversaries, pick one to write about:
Streptococcus pyogenes
A small, Gram-positive coccus that infects individuals and causes strep throat among other illnesses. It is an extracellular pathogen, binding to cell surfaces and invading the body.
| Virulence factor/antigen | Made from | Effect on the host |
| Capsule | Polysaccharide | Slows down phagocytosis by making it difficult for phagocytes to grab onto the cells. |
| M-Protein | Protein | Causes specific, strong attachment, to the surface of the tonsil. This attachment is much stronger than capsule binding |
| lipoteichoic acid present in the cell wall | Lipid and teichoic acid | Aids in the initial attachment to the tonsil cells on the surface of the throat. |
| Hyaluronidase | Protein (enzyme) | Degrades the hyaluronic acid present between host cells and helps bacteria invade tissues |
| Streptokinase | Protein (enzyme) | Breaks down fibrin clots in the blood that try to trap the bacterium |
Staphylococcus aureus
A Gram-positive coccus that can cause a large number of different types of illness. It is known for causing infections of the skin and eye, but can also penetrate to deeper tissues. Invasive cases of the disease can become life-threatening. It is also an extracellular pathogen.
| Virulence factor/antigen | Made from | Effect on the host |
| Protein A | Protein | Binds to the conserved side of antibodies, making it more difficult for the cell to use these antibodies against the microbe |
| nucleases, proteases, lipases, and collagenase | Protein | Degrade host tissues and make them available as nutrients for the cell |
| hyaluronidase | Protein | Degrades the hyaluronic acid present between host cells and helps bacteria invade tissues |
| Cell wall teichoic acid | Teichoic acid | Aids in attachment to cells |
| α-hemolysin | Protein | A toxin that enters host cell membranes and causes pore formation. This causes major damage to the host. |
Rhinovirus
The rhinovirus family of viruses (there are over 160 known types that infect humans) is one major cause of the common cold. They infect the upper respiratory tract and cause misery worldwide. It is composed of a single-stranded RNA molecule that can be translated at the ribosome of the host (the viral genome contains the coding strand). This RNA molecule encodes the four proteins that form the outside cover of the virus (its capsid) and a viral polymerase to copy the genome. The Rhinovirus is an intracellular pathogen (it grows inside of cells) and requires a different type of response from the immune system. Viruses don't have the same kind of virulence factors, but they do have proteins that are displayed to the immune system. Remember that the immune system will encounter these proteins in different ways. The capsid will be present on free virus moving to new cells in the respiratory tract. The capsid and RNA polymerase will be displayed in MHCI molecules of infected cells.
| Virulence factor/antigen | Made from | Effect on the host |
| Capsid proteins | Protein | These bind to and recognize the host by binding to Inter-Cellular Adhesion Molecule 1 or to Cadherin-related family member 3 protein, depending upon the viral species (A, B, or C). These receptors are found on cells of the respiratory epithelium. |
| RNA polymerase | Protein | The enzyme that replicates the DNA. |
In your essay I want you to answer the following questions. You can do this explicitly or implicitly:
- Name one part of innate immunity that could prevent infection by your chosen pathogen.
- What parts of the immune system are involved in recognizing each virulence factor/antigen? You may use the same immune system part to counteract several different virulence factors/antigens
- What is more important for stopping this infection, humoral (antibodies) or cell-mediated immunity? Why do you think so?
- What cells are involved in taking care of the bacteria or infected cell and how do they do it?
- Write up your response to these questions and submit it for grading. The total text that you submit should be no more than 400 words, but a good effort may end up being less than 400 words.
Please make sure to write this in simple terms, not sounding advanced. This is a beginner micro biology class and I am not very educated in this subject. Let me know if you have any questions. Thank you!