11. Immune System Flashcards
1
Q
Nonspecific First Line of Defense:
A
- general defense, not specific (innate)
- skin: physical and hostile barrier covered with oily and acidic (ph 3-5) secretions from sweat glands.
- Antimicrobial proteins: lysozyme (saliva, tear) which breakdown cell wall of bacteria.
- Cilia: line the lungs, serve to sweep invaders out
- Gastric juice: stomach kills most microbes
- Symbiotic bacteria: digestive tract and vagina outcompetes many other organisms.
2
Q
Second Line of Defense:
A
- several nonspecific mechanisms (innate):
1. Phagocytes: (WBCs, leukocytes) engulf foreign particles/bacteria/dead/ or dying cells by phagocytosis. NEUTROPHILS destroy pathogens of infected tissues. MONOCYTES move into tissues and develop into large phagocytic cells called macrophages. other WBCs called Natural killer cells (NK cells) attack abnormal body cells (ex. tumors) or pathogen-infected body cells.
2. Complement: group of about 20 proteins that “complement” defense reactions. these proteins help attract phagocytes to foreign cells and help destroy foreign cells by promoting cell lysis.
3. Interferons: substances secreted by cells invaded by viruses that stimulate neighboring cells to produce proteins that help them defend against the viruses.
- Inflammatory response: nonspecific events that occur in response to pathogens. ex. when skin is damaged and bacteria enters body, following may occur:
a. histamine secreted by BASOPHILS, WBCs found in connective tissue
b. vasodilation: stimulated by histamine, increase blood supply to damaged area and allow easier movement of WBCs through vesels. This also causes redness, an increase in temp, and swelling. Increase in temp –> like a fever may stimulate WBCs and may make the environment inhospitable to pathogens.
c. phagocytes: attracted to injury by chemical gradients of complement, arrive and engulf pathogens and damaged cells
d. complement: help phagocytes engulf foreign cells, stimulate basophils to release histamine and help lyse foreign cells.
3
Q
Third line of defense
A
IMMUNE RESPONSE
- differs from inflammatory response in that it targets specific antigen (any foreign substance).
4
Q
Antigen
A
- any molecule, usually a protein or polysaccharide that can be identified as foreign.
- may be a toxin (sting of an insect)
5
Q
Major Histocompatibility Complex (MHC)
A
- mechanism by which immune system is able to differentiate between self and nonself cells.
- collection of glycoproteins that exists on membranes of all body cells. Very unique, except for identical twins, rare for two people to have same set of MHC molecules.
6
Q
Primary agents of immune response:
A
- Lymphocytes, WBCs (leukocytes) that originate in bone marrow (like all blood cells) but concentrate in lymphatic tissue such as lymph nodes, thymus gland, and spleen.
7
Q
Various kinds of lymphocytes:
A
- B cells
2. T cells
8
Q
B Cells
A
- lymphocytes that originate and mature in bone marrow (B for bone). They respond to antigens. Plasma membrane of surface B cells is characterized by specialized antigen receptors called antibodies
- When B cells encounter antigens that specifically bind to their antibodies, B cells proliferate, producing two kinds of daughter B cells:
1. Plasma cells; B cells that release their specific antibodies which then circulate through the body, binding to antigens
2. Memory cells: long-lived B cells. Do not respond immediately to antigen invasion. Instead, circulate the body and respond quickly to eliminate any subsequent invasion by the same antigen.
9
Q
Properties of Antibodies (or Immunoglobulins):
A
- they are proteins
- each antibody is specific to a particular antigen
- 5 classes of antibodies (or immunoglobulins): IgG, IgM, IgA, IgE, IgD (good morning america eat d***). each associated w/ particular activity.
- each class is a variation of a basic Y-shaped protein that consists of constant regions and variable regions. Variable regions are sequences of amino acids that give specific specificity to antigens.
- Antibodies inactivate antigens by binding to them. Inactivation is followed by macrophage phagocytosis. In addition, by binding to surface antigens of nonself cells, antibodies stimulate complement proteins to bring about lysis of pathogens.
10
Q
T cells
A
- originate in bone marrow, but mature in thymus (T for thymus)
- Like B cells, plasma membranes of T cells have antigen receptors. However, these receptors are NOT antibodies, but recognition sites for molecules displayed by nonself cells.
- Self and nonself are distinguished as follows:
a. MHC markers on plasma membranes of cells distinguish self and nonself
b. When a body cell is invaded by a virus/foreign cell/antigen, the body cell displays a combination of self and nonself markers. T cells interpret this abberant display of markers as nonself.
c. Cancer cells or tissue transplant cells, or other cells that display aberrant markers are recognized as nonself cells by T cells. - When T cells encounter nonself cells, they divide and produce two kinds of cells:
a. Cytotoxic T cells (or Killer T cells) recognize and destroy nonself cells by puncturing them –> lyse
b. Helper T cells stimulate proliferation of B cells and cytotoxic T cells.
11
Q
Clonal Selection
A
- When an antigen binds to a B cell or when a nonself cell binds to a T cell, the B cell or T cell begins to divide, producing numerous daughter cells, all identical copies of the parent cell. This process is called CLONAL SELECTION, since only the B or T cell bearing the effective antigen receptor is “selected” and reproduces to make clones or identical copies of itself.
- clonal selection results in a proliferation of B cells and T cells that will engage a specific, invading antigen.
12
Q
Responses to immune system are categorized into two kinds of reactions:
A
- Cell-mediated response
2. Humoral response (or antibody-mediated response)
13
Q
Cell-mediated response
A
- uses mostly T cells and responds to any nonself cell, including cells invaded by pathogens.
- When a nonself cell binds to a T cell, the T cell undergoes clonal selection, initiating the following chain of events:
a. T cells produce cytotoxic T cells (killer T cells)
b. T cells produce helper T cells
c. Helper T cells bind to macrophages. Macrophages that engulfed pathogens display aberrant plasma membrane markers, Helper T cells bind these “nonself” markers
d. Helper T cells produce interleukins to stimulate a proliferation of T cells and B cells. When helper T cells bind macrophages, they release interleukins –:> positive feedback that results in proliferation of interleukins, macrophages, helper T cells, B cells, and cytotoxic T cells.
14
Q
Interleukins
A
- Produced by Helper T cells
- communication chemicals “between leukocytes”
- initiate a sequence of positive-feedback that result in proliferation of interleukins, macrophages, helper T cells, B cells, and cytotoxic T cells
15
Q
Humoral Response (antibody-mediated response)
A
- involves most cells and responds to antigens or pathogens that are circulating in the lymph or blood.
- “humor” is medieval term for body fluid
- Includes following events:
a. B cells produce plasma cells. Plasma cells in turn, release antibodies that bind with antigens or antigen-bearing pathogens.
b. B cells produce memory cells. Memory cells provide future immunity.
c. Macrophage and helper T cells stimulate B cell production. In many cases, antigen will not directly stimulate proliferation of B cells. Instead, antigen or anigen-bearing pathogen englufed by macrophage –> T cell bind macrophage in cell-mediated response –> interleukins secreted by helper T cells stimulate production of B cells.
