Question

The first line of defense is composed of structures, chemicals and processes that prevent microbes from entering the body. Skin, mucous membranes and the microbiome help to prevent infection. Compromise of one of these components may provide a way for microbes to infect the body. The skin is a complex and large organ made of nerves, blood vessels, sebaceous glands, hair follicles and an outer layer of dead cells, the epidermis. The epidermis flakes off, which prevents colonization, contains dendritic cells phagocytes which alert the adaptive immune system of foreign cells and antimicrobial chemicals, e.g. dermicidins, lysozyme. Mucous membranes cover body cavities that are exposed to the environment, these membranes have two layers the epithelium and connective tissue. Because the epithelial layer is thinner than the multiple layers of skin, mucous membranes are a less effective barrier to the entrance of pathogens. Some mechanisms epithelium use are continual shedding of cells, mucous secreted by goblet cells, ciia in the respiratory tract which propels mucous and trapped particles away from the lungs and antimicrobial peptides i.e. lysozyme.

1. Explain succintly how hyaluronidase and gelatinase enable bacteria to become invasive. p423

2. Describe one example of an adhesion factor and include how it permits the microbe to penetrate the first line of defense. p418

Defensins are prevalent in many organisms because they defend against microbial infection. Defensins may punch holes in cytoplasmic membranes of microbes, interrupt cell signalling in microbes, may recruit cells of the immune system to fight off the microbe or be enzyamtic in destroying microbes virulence factors.

3. Repeated hand washing is effective infection control, however it might lead to cracked skin. Why are cracks in the skin of hands problematic in healthcare workers?

The second line of defense is really interesting because it involves cells of the blood system, which all originate from stem cells in the bone marrow but differentiate into very different types of cells. For example phagocytes, more about these cells later, may contain Toll like receptors and NOD proteins which detect foreign things in the area and send warning signals to certain cells in the immune system that could mount a defense.

4. Toll like receptors have been targeted with certain drugs in a treatment for lower back pain. How might a Toll like receptor be able to induce an immune response that might lead to lower back pain. Be creative, take the information on p. 453-454, and think about which one of the possible effects of Toll like receptor signalling might cause pain. Remember one treatment for lower back pain is injection of steroids, why do steroids reduce lower back pain?

Interferons are cytokines made by one virally infected cell and released into the extracellular space to warn neighboring cells a virus has invaded the neighborhood. Actually there are two types of interferons, Type I and Type II, this discussion will focus on Type I. Please reveiw the material on page 454-455 to fill in the gaps. So once a neighboring cell recieves the cytokine signal that a virus is in the nieghborhood, that cell now has notice of the viral threat and begins to transcript the genes for anti-viral proteins.

5. What is produced by the cell that transcribes genes for anti viral protiens? How is this preparation for viral attachment and entry? Will this cell still be vulnerable to attachment and entry by the virus that have infected neighboring cells?

Answer 1

1. Gelatinase is a proteolytic enzyme, it breaks down collagen tissue and thus microbe spreads throughout the body. Hyaluronidase breaks hyaluronic acid (HA). SOME bacteria depends on HA capsule to evade phagocytosis and to interact with epithelial cells.

2. Adhesion factor is important virulence factor in bacteria. It is required to colonize new host e.g., multivalent adhesion molecules (MAMs) contain tandem repeats of mammalian cell entry domains that binds to extracellular matrix proteins and abiotic lipids on host tissues.

3 it is because skin has barrier of oils and lipids that protects against external agents. Frequent washing causes the natural barrier to strip away.

4. Toll-like receptors trigger pro-inflammatory central immune signaling events and cause heightened pain. It dysregulates several functions that are important to maintain homeostasis.

5. The first line of defence is production of IFNs ( interferons)

It mainly causes degradation of viral infection.

No, this cell is not vulnerable to attachment and entry by viruses as interferons are used for communication between cells to trigger immune system, thus antiviral state is induced in neighbouring cells too.