Chapter 18 Pathological consequences of infection Flashcards
Seven viruses that infect humans can cause up to 15% of human cancers around the world. Which one leads to cervical cancer?
Human papillomaviruses
What bacteria cause the #1 pathogen-associated disease in the world, and what does it cause?
Streptococcus mutant produces acid which degrades tooth enamel, leading to tooth decay
List the modes of action of toxins and their consequences.
- enzymatic lysis ->cell death
- pore formation -> cell death
- inhibition of protein synthesis ->cell death
- hyperactivation by V. cholerae -> high Na and H2O loss -> diarrhea
- effects on nerve-muscle transmission: Cl. tetani toxin blocks release of inhibitory transmitter->continuous stimulation; Cl. botulinum toxin blocks release of Ach from vesicles ->stimulation blocked
Why do bacteria secrete enzymes, and what kinds of enzymes do they secrete?
A number of bacteria release enzymes that break down the tissues or the intercellular substances of the host, allowing the infection to spread freely (promote bacterial survival or spread). Among these enzymes are hyaluronidase, collagenase, DNase and streptokinase.
Some staphylococci release a coagulase, which deposits
a protective layer of fibrin onto and around the cells (protecting from environment) , thus localizing them.
What do the some of most successful vaccines consist of? What are the classic examples?
toxoids made from toxins that are inactivated without altering their antigenicity. Diphtheria and tetanus toxoids.
What is more highly conserved- toxins or surface antigens, and what does this allow for?
toxins are generally more highly conserved in their structure than the surface antigens or the organism secreting them, which allows for more effective cross-immunity. This explains why scarlet fever (caused by streptococcal erythrotoxin) usually occurs only once, whereas streptococcal infections recur almost indefinitely.
Out of the bacteria that cause food poisoning due to pre-formed toxin in food, which ones did the professor say form spores?
Bacillus and Clostridium
Which bacterial endotoxin activates almost every immune mechanism and what is its important in fever and shock?
LPS, also activates the clotting pathway, also clinically important in fever and shock
What is a typical LPS endotoxin composed of?
- a conserved lipid portion (lipid A) inserted into the cell wall, responsible for much of the toxic activity
- a conserved core polysaccharide
- the highly variable O-polysaccharide, responsible for the serological diversity which is a feature of organisms such as salmonellae and shigellae.
What is the difference between endotoxins and an exotoxins?
Unlike exotoxins, endotoxins are integral parts of the microbial cell wall and are normally released only when the cell dies. Endotoxins are particularly characteristic of Gram-negative bacteria.
What is the principal mechanism for Type I hypersensitivity (allergic/anaphylactic)?
IgE, mast cells
What is the principal mechanism for Type II hypersensitivity (cytotoxic)?
IgG (to surface antigens, complement, cytotoxic cells). Type II reactions are mediated by antibodies to the infectious organism or autoantibodies
Briefly describe the pathogenesis of type I hypersensitivity.
IgE binds to mast cells, leading to release of vasoactive amines
What is the principal mechanism for Type III hypersensitivity (immune complex-mediated), phases of the disease an examples?
Immune complexes cause disease when they become lodged in tissues or blood vessels (also involves IgG)
1. formation of Ag-Ab complexes in the circulation
2. Deposition of immune complexes in various tissues
3. Inflammatory reaction and destruction of host tissues.
Examples: SLE, streptococcal gloemrulnephritis, polyarteritis nodosa, reactive arthritis, “serum sickness”
What is the principal mechanism for Type IV hypersensitivity (cell-mediated)?
Cell-mediated responses with the activation of both T cells and macrophages invariably cause some tissue destruction (granuloma formation)
CD4+ T cells (and sometimes CD8+ cells) respond to tissue antigens by secreting cytokines that stimulate inflammation and active phagocytes, leading to tissue injury.
In some diseases, CD8+CTLs directly kill tissue cells.
