The Immune System Flashcards
In innate immunity, recognition and response rely on traits common to groups of
pathogens.
In adaptive immunity, receptors provide
pathogen-specific recognition.
Adaptive immunity defends against infection of
body fluids and body cells.
What do we mean by innate immunity?
Includes barrier defenses, molecular recognition relies on small set of receptor proteins that bind to molecules or structures that are absent from animal bodies but common to a group of viruses, bacteria, or other microbes
Binding of an innate immune receptor to a foreign molecule activates internal defenses, enabling responses to a very broad range of pathogens
What has helped make insects so successful in their habitats, which are teeming with diverse microbes?
Exoskeleton composed of chitin, which also lines the insects intestines, where it blocks infection by many pathogens ingested with food
How about their digestive systems?
Lysozyme, an enzyme, also protects digestive system
How about their hemolymph? What’s hemolymph? What are hemocytes and what do they do?
Hemocytes travel in hemolymph which ingest and break down bacteria and other foreign substances by phagocytosis
Can also release chemicals that kill pathogens and secrete peptides that kill fungi and bacteria through their plasma membranes
Innate immunity is found in all animals (and plants as well). What do we mean by innate immunity?
includes barrier defenses, molecular recognition relies on a small set of receptor proteins that bind to molecules or structures that are absent from animal bodies but common to a group of viruses, bacteria, or other microbes
What has helped make insects so successful in their habitats, which are teeming with diverse microbes?
They rely on their exoskeleton as a first line of defense against most pathogens
How about insects exoskeletons?
it is the first line of defense against infection
How about insects digestive systems?
Chitin lines the intestine where it blocks infection by many pathogens ingested with food;
Lysozyme is an enzyme that breaks down bacterial cell walls,
How about insects hemolymph? What’s hemolymph? What are hemocytes and what do they do?
hemolymph- the circulatory fluid
hemocytes- immune cells travel throughout the body in the hemolymph- some ingest and break down bacteria and other foreign substances through phagocytosis
What is it about fungi and bacteria that that serve as identity tags that are recognized by insect immune cells?
fungal cell was contain certain unique polysaccharides, whereas bacterial cell walls have polymers containing combinations of sugars and amino acids not found in animal cells
How does the immune cell detect these identity tags?
insect immune cells secrete recognition proteins, each of which binds specifically to a macromolecule characteristic of a broad class of bacteria or fungi
What happens when the Toll receptor or some other recognition protein on the surface of the immune cell is activated?
signal transduction from the Toll receptor to the cell nucleus leads to synthesis of a set of antimicrobial peptides active against fungi
In mammals, epithelial tissues block the entry of many
pathogens.
What are some of the physical defense barriers associated with epithelial tissues? How about skin? How about mucus membranes? How about ciliated epithelial cells in the trachea? How about saliva, tears, and mucus secretions?
Block the entry of many pathogens; the mucous membranes produce mucus, a viscous fluid that traps pathogens and other particles. In the airway, violated epithelial cells sweep mucus and any entrapped material upward, helping prevent infection of the lungs. Saliva, tears, and mucous secretions that bathe various exposed epithelia provide a washing action that also inhibits colonization by fungi and bacteria
Beyond their physical role in inhibiting microbial entry, body secretions create an environment that is ___ to many microbes.
hostile
What is in tears, saliva, and mucus that destroys cell walls of susceptible bacteria?
Lysozyme which destroys the cell walls of susceptible bacteria as they enter the openings around the eyes or the upper respiratory tract
What’s the deal with the stomach?
the acidic environment of the stomach kills most microbes in food or water before they can enter the intestine
How about the pH of human skin?
ranges from 3-5, acidic enough to prevent the growth of many bacteria
Pathogens entering the mammalian body are subject to
phagocytosis.
How are invading pathogens detected by phagocytic cells? What gives this system specificity as to recognizing different types of pathogens?
receptors; Toll-like receptor binds to fragments of molecules normally absent from the vertebrate body but characteristic of a set of pathogens
The two main types of phagocytic cells in the mammalian body are
neutrophils and macrophages.
What do neutrophils and macrophages do?
neutrophils circulate in the blood, are attracted by signals from infected tissues and then engulf and destroy the infecting pathogens some Macrophages (larger phagocytic cells) migrate through the body where others reside permanently in organs and tissues where they are likely to encounter pathogens
What do dendritic cells and eosinophils do?
mainly populate tissues, such as skin, that contact the environment. They stimulate adaptive immunity against pathogens they encounter and engulf
What do natural killer cells do?
circulate through the body and detect the abnormal array of surface proteins characteristic of some virus-infected and cancerous cells. Do not engulf cells- instead release chemicals that lead to cell death
Many cellular innate defenses of vertebrates involve the ___ system.
lymphatic
How are macrophages and dendritic cells associated with the lymphatic system?
Some macrophages reside in lymph nodes, where they engulf pathogens that have entered the lymph from the interstitial fluid.
Dendritic reside outside the lymphatic system but migrate to the lymph nodes after interacting with pathogens
In mammals, pathogen recognition triggers the production and release of a variety of peptides and proteins that attack ___ or impede their ___.
pathogens; reproduction
What are interferons and what do they do?
proteins that provide innate defense by interfering with viral infections; virus-infected body cells secrete interferons, which induce nearby unfitted cells to produce substance that inhibit viral replication
What is the complement system and what does it do?
consists of roughly 30 proteins in blood plasma- these proteins circulate in an inactive state and are activated by substances on the surface of many microbes. Activation results in a cascade of biochemical reactions that can lead to lysis of invading cells
A local inflammatory response involves changes that are brought about by signaling molecules released upon
injury or infection.
What are the signaling molecules? What do they do?
what is released upon injury or infection and they induce the inflammatory response
Why does an inflammatory response involve redness, increased temperature, and swelling at the site of the injury?
enhanced blood flow helps deliver antimicrobial peptides
What is pus?
a fluid rich in white blood cells, dead pathogens, and cell debris from damaged tissue
What are the systemic responses that can result from severe injury or infection? What is septic shock?
cells secrete molecules that stimulate the release of additional neutrophils from bone marrow. in severe infection, the number of white blood cells in the bloodstream may increase several fold within only a few hours- also fever;
high fever,low bp, and poor blood flow through capillaries
What are some of the ways that pathogens can evade the innate immune system?
an outer capsule, resist breakdown within lysosomes
Vertebrates are unique in having adaptive immunity in addition to
innate immunity.
The major players in adaptive immunity are B cells and T cells, which are types of white blood celled called
lymphocytes.
Where and from what do lymphocytes originate?
from stem cells in the bone marrow
What’s the deal with lymphocytes that mature into T cells?
the stem cells migrated from the bone marrow to the thymus and turned to T cells
What’s the deal with lymphocytes that mature into B cells?
These cells remained and matured in the bone marrow and developed into B
What is an antigen? What is an epitope? What is an antigen receptor? What does this have to do with B cells, T cells, and pathogens?
Any substance that elicits a B or T cell response; a protein where the B or T cell binds to the antigen
What are B cell receptors like?
a Y-shaped molecule consisting of four polypeptide chains: 2 identical heavy chains and two identical light chains, with disulfide bridges linking the chains together; A transmembrane region near one end of each heavy chain anchors the receptor in the cell’s plasma membrane. A short tail region at the end of the heavy chain extends into the cytoplasm
What’s the deal with the constant regions?
where amino acid sequences vary little among the receptors on different B cells. includes the cytoplasmic tail and transmembrane region of the heavy chain and all of the disulfide bridges
What’s the deal with the variable regions?
Its amino acid sequence varies extensively from one B cell to another; Together, parts of a heavy-chain V and a light-Chain V region form an asymmetric binding site for an antigen
What’s the deal with the antigen-binding sites?
Each B cell antigen receptor has two identical antigen-binding site; a specific lock and key
How are our B cells able to recognize so many different pathogens?
?they can only bind to one specific shape?
How does the B cell recognizing the pathogen?
?they can only bind to one specific shape?
What is the B cell doing after it has interacted with the surface antigen of the pathogen?
it secretes a soluble form of the receptor; this protein is known as an antibody
What is interesting about the antigen-binding site of the antibodies being produced?
they have the same Y-shape structure as B cll but a secreted rather than membrane bound
What is it that is actually defending against pathogens?
antibodies
How are antigen receptors on T cells different from those on B cells? How are they the same?
only 2 chains not 4 so it doesn’t make Y shape;
both have V and C regions
B cells recognize pathogens directly. What do T cells recognize?
they bind to fragments of antigens that are displayed on the surface of host cells
Each person makes more than 1 million different B cell antigen receptors and 10 million different T cell antigen receptors. Given that there are only about 20,000 protein-coding genes in the human genomes, how is this possible?
The answer has to do with gene rearrangement. We will consider an immunoglobulin (Ig) gene that encodes the light chain of both secreted antibodies and membrane-bound B cell antigen receptors. However, all B and T cell antigen receptor genes undergo very similar transformations.
What is the DNA of an undifferentiated B cell like?
a variable (V) segment, a joining (j)m and a constant (C) segment
How many combinations of one V, one J, and one C are there?
40 V x 5 J x 1 C = 200 combinations of one each.
What is the DNA of a differentiated B cell like? This is only one of 200 possibilities. What happens next?
?
The number of heavy chain combinations is even greater. Each pair of randomly rearranged heavy and light chains results in a different antigen-binding site. For the total population of B cells in the human body, the number of such combinations has been calculated as
3.5 x 106.
When a B cell interacts with a pathogen or free antigen, or a T cell interacts with an antigen-presenting cell, the B cell or T cell proliferates, forming a clone of identical cells. , this process is called
clonal selection.
What is the result of clonal selection?
When T cells undergo it, they generate memory T cells and effector T cells
___ ___ is responsible for the long-term protection that a prior infection or vaccination provides against many diseases, such as chicken pox.
Immunological memory
What is a primary immune response?
peaks about 10-17 days after the initial exposure; The production of effector cells from a clone of lymphocytes during the first exposure to an antigen
What is a secondary immune response?
When the individual is exposed again to the same antigen, the response is faster
With B cells, how can the primary and secondary responses be distinguished from one another?
?
(Chart)What do you see with regard to antibodies to A?
The secondary immune response is much faster than primary
(chart)What do you see with regard to antibodies to B?
Only shows a primary immune response
What does this mean to you if you come into contact with a pathogen for the first time? How about for the second time?
It will take longer to produce effector cells the first time; but the second time you will recover much faster
The secondary immune response relies on the reservoir of T and B memory cells generated following initial exposure to an antigen. Because these cell are long-lived, they provide the basis for ___ ___, which can span many decades.
immunological memory
What is a humoral immune response?
occurs in the blood and lymph; antibodies help neutralize or eliminate toxins and pathogens in the blood and lymph
What is a cell-mediated immune response?
specialized T cells destroy infected host cells
What is the pivotal role of helper T cells?
they trigger both the humoral and cell-mediated immune responses; they do not carry out response- they initiate production of antibodies that neutralize pathogens and activate T cells that will kill the infected cells
What is an antigen-presenting cell?
can be a dendritic cell, macrophage or B cell
How do helper T cells recognize the various antigen-presenting cells (dendritic cells, macrophages, and B cells) as opposed to other infected host cells displaying antigens? Keep an eye out for the different classes of MHC molecules as we move on.
Most body cells have only class I MHC molecules, but antigen-presenting cells have Class I and class II MHC molecules; the Class II provide a molecular signature by which an antigen-presenting cell is recognized
What’s the deal with the class II MHC molecule?
It is how antigen presenting cells are recognized; keeps the cells (antigen-presenting and Tcells) joined
How do cytotoxic T cells work against infected cells?
use toxic proteins to kill cells infected by viruses or other intracellular pathogens before pathogens fully mature
Let’s look at the progression of cytotoxic T cell action. By the way, notice anything interesting about the MHC molecule here?
The bind to the class I MHC molecules on the infected cell surface
Let’s look at the progression of B cell activation
Activation of B cells involves both helper T cells and proteins on the surface of pathogens. Stimulated by both an antigen and cytokines, the B cell proliferates and differentiates into memory B cells and antibody-secreting plasma cells
Antibodies do not actually kill pathogens, but by binding to antigens on the pathogen surface they interfere with pathogen activity or mark pathogens in various ways for
inactivation or destruction.
What happens with neutralization?
process in which antibodies bind to proteins on the surface of a virus then precent the infection of a host cell.
What happens with opsonization?
antibodies bound to antigens on bacteria do not block infection, but instead present a readily recognized structure for macrophages or neutrophils, thereby promoting phagocytosis
What happens with activation of complement system and pore formation?
Binding of a complement protein to an antigen-antibody complex on a foreign cell triggers the generation of a membrane attack complete that forms a pore in the membrane of the cell; Ions and water rush into the cell, causing it to swell and lyse
