AP Bio Chapter 43**
What are pathogens? Why is it necessary to prevent them from colonizing our bodies? If they do colonize, what effects would they have?
- Pathogens= agents that cause disease -
What general defense mechanisms does the body use to help prevent colonization by pathogens? For example, what general defense mechanisms are involved in local inflammatory response?
- Skin and mucous membranes -> physical barriers -
Complement system-
30 proteins that cause lysis of pathogenic cells when activated
B. What surface molecule on a cytotoxic T cell assist in the interaction with a class I MHC molecule displayed on infected cells?
Accessory protein
Sketch a B-cell receptor............... How do the positions of the disulfide bridges, transmembrane regions, and antigen binding sites relate to the location of the variable and constant regions?
Antigen binding sites- near V regions Disulfide bridges- near C regions Transmembrane regions- near C regions and in plasma membrane
A. What surface molecule of a helper T cell facilitates the interaction with a class II MHC molecule of an antigen-presenting cell and the helper T cell?
Antigen receptor
In myasthenia gravis, antibodies bind to and block acetylcholine receptors at neuromuscular junctions, preventing muscle contraction. Is this disease best classified as an autoimmune disease, immunodeficiency disease, or an allergic reaction? Explain.
Autoimmune disease- produces antibodies against self molecules.
Describe the differences between the antigens that B cell receptors and antibodies recognize and the antigens that T cell receptors on cytotoxic T cells and helper T cells recognize.
B cells and antigens recognize epitopes. T cells on cytotoxic T cells and helper T cells recognize MHC molecules.
A. Why is AIDS such a deadly disease?
Because it attacks cells that fight off infections thereby weakening the immune system.
Treatment of antibodies with a particular protease clips the heavy chains in half, releasing the two arms of the Y-shaped molecule. How might the antibodies continue to function?
Because the antigen binding sites are still intact, they could neutralize viruses and opsonize bacteria.
B. Why has it proved so difficult to prevent and cure this disease?
Because through research and trials, scientists have realized weakened strains of the virus can still cause AIDS, and dead strains provide no protection at all.
Macrophages-
Circulate through body/tissues and engulf pathogens
People with herpes simplex type 1 viruses often get mouth sores when they have a cold or similar infection. How might this location benefit the virus?
Colds usually cause oral secretions that can aid in viral transfer.
A. How is the great diversity of B and T cells produced?
Combinations of J, V, and C segments
C. What does an activated helper T cell release?
Cytokines
Lysozyme-
Destroy cell walls of bacteria
Neutrophils-
Engulf and destroy infecting pathogens
Suppose that a snake handler bitten by a particular venomous snake was treated with antivenin. Why might the treatment for a second such bite be different?
If the handler developed immunity to the antivenin from the previous treatment, injected him again would lead to a more extreme immune response.
How does HIV affect the immune system?
It significantly weakens the immune system.
Explain two advantages of having memory cells when a pathogen is encountered for a second time?
Memory cells ensure that a receptor specific for that epitope will be present and there will be more lymphocytes with this specificity.
List three ways in which antibodies mediate the disposal of antigens:
Neutralization, opsonization, and activation of complement system and pore formation.
D. What does a cytotoxic T cell attached to an infected body cell release?
Perforin
Eosinophils-
Populate underneath mucousal surfaces and discharge destructive enzymes when encountered by a pathogen
Interferons-
Proteins that directly interfere with viral infections
Although pus is often seen simply as a sign of infection, it is also an indicator of immune defenses in action. Explain.
Pus consists of white blood cells, cell debris, and fluid and is indicative of an inflammatory response to an infection.
Natural killer cells-
Release chemicals to cause cell death and prevent spread of cancer/virus
Mast cells-
Secrete histamine to initiate inflammatory response
Histamine-
Signal inflammatory response
If a child were born without a thymus, what cells and functions would be deficient? Explain.
T cells would be deficient, and
If both copies of a light chain gene and a heavy chain gene recombined in each B cell, how would this affect B cell development?
The different combinations would create 4 different receptors, and if any one was self reactive, the lymphocyte would be eliminated in the generation of self toleration. So, more B cells would be eliminated, and those that weren't would be less effective because of the variety of receptors they express.
If a microbe grew optimally at a low pH, how might this affect its ability to act as a human pathogen? Explain.
The microbe couldn't survive in the more acidic bodily environments, such as the stomach, so it wouldn't be very successful in humans.
Describe one invertebrate defense mechanism and discuss how it is an evolutionary adaptation retained in vertebrates.
Toll-like Receptors- descended from Drosophila TLR; retained because they can easily identify molecules not characteristic to vertebrates(i.e. double stranded RNA, lipopolysaccharides)
Dendritic cells-
Usually populate tissues with contact to environment; cause adaptive immunity against engulfed pathogens
If about 10^5 genes are available in the human genome to produce proteins, how can we produce more than 10 X 10^6 different kinds of Ab receptors (proteins) on B cells?
Various combinations of J, V, and C segments.
C. Describe clonal selection.
When an antigen binds to a receptor on a cell, that specific cell proliferates into clones. So, antigen binding SELECTS which lymphocyte will divide and produce a CLONAL population.