Lecture 4: Immune System Flashcards
main goals of the immune system
fight pathogens (such as bacteria and viruses) and inflammation, detect mutated cells, repair damaged tissue, and clean up dead and damaged cells
non-specific immune response
the body has the same reaction to different pathogens, and does not change over time
specific (adaptive) immune response
the body produces a specific response to eliminate a unique pathogen
- this response becomes progressively stronger
- the immune system can react quickly when a virus enters the body for the second time
white blood cells
protect the body from infection
- many of these cells are called luekocytes
- patrol the body, looking for signs of infection or abnormalities, such as mutated cells
platelets
play an important role in blood clotting
- all cells originate in the bone marrow, from a primordial cell that can differentiate
red blood cells
responsible for carrying oxygen from the lungs to the rest of the body and bringing carbon dioxide back to the lungs for exhalation
- unlike white blood cells and platelets, red blood cells do not play a direct role in the immune system
- called erythrocytes
infectious diseases
- bacteria: salmonella, chlamydia, etc.
- viruses: HIV, covid
- protozoa (very small worms): malaria, giardia
- fungi: candidiasis, trichophyton
what you can get sick from
- infectious diseases
- allergic reactions
- autoimmune diseases
non-communicable diseases
cancer, diabetes, cardiovascular disease, and COPD (asthma, bronchitis)
virus
consists of hereditary material in a casing (coat) that is able to reproduce by using the reproductive apparatus of living organisms (hosts)
- needs a cell from another organism in order to replicate itself
- binds to the cell and the information from the virus enters the cell making copies of DNA and RNA
- proteins are produced that allow new viruses to emerge and spread
defense against viruses
the skin, mucous membranes and acidity, and parts of the innate immune system can keep viruses and bacteria from taking over the body
infections
a virus must ‘take over’ a cell in order to replicate (cause an infection)
how infected cells die
- lysis (burst)
- apoptosis (programmed cell death or ‘suicide cell’)
viral infection
a specific type of infection caused by a virus
- the virus enters the body, invades host cells, and uses them to replicate and cause disease
- often require specific treatments
virus replication cycle
- adhesion
- penetration
- non-coating
- replication
- assembly
- release
adhesion
the virus attaches to the surface of a host cell by binding to specific receptors on the cell membrane
penetration
after attachment, the virus enters the host cell through endocytosis or membrane fusion
non-coating
the viral capsid breaks down, releasing the viral genome (DNA or RNA) into the host cell
replication
- DNA viruses use host cell proteins and enzymes to create additional DNA used to copy the genome or is transcribed into mRNA
- RNA viruses typically use the RNA core as a prototype for the synthesis of viral genomic RNA and mRNA
assembly
new viral particles are assembled by packaging the replicated genome and proteins into new capsids and create new virions
release
the new virions are released into the host system, where they can infect adjacent cells and repeat the replication cycle
- some are released when the host cell dies and other infected cells are left behind by crossing the membrane without directly killing the cell
vaccines
can be formed by using attenuated live viruses, killed viruses, or molecular subunits of the virus
live vaccines
usually made by weakening the ‘wild-type’ (disease-causing) virus by growing it in the laboratory in tissues or at temperatures different from what the virus is used to in the host
- allow the immune response to develop in time to prevent serious disease
- low but significant risk of these viruses returning to their pathogenic form through back mutations
antiviral drugs
often have a limited ability to cure viral diseases, but are used to control and reduce symptoms for a wide variety of viral diseases
- inhibit the virus by blocking the function of some of its proteins
vertebrate immune system
a complex system of defence against external and internal threats to the integrity of the body
- divided into the innate immune system and the adaptive immune system
innate immune system
not specific to a particular type of pathogen
- not caused by infection or vaccination and depends primarily on physical and chemical barriers that work on all pathogens
- first line of defence
adaptive immune system
links a very specific response to substances and organisms that do not belong in the body
- lasts longer and has a memory system that allows it to react with greater intensity if the body encounters a pathogen again, even years later
the skin
contains the protein keratin which prevents physical access to cells
- the surface of the skin is acidic preventing bacterial growth
mucous membranes
sticky mucus provides a physical trap for pathogens, preventing them from entering deeper into the body
hair
hairs protect the openings of the body, such as the nose and ears, from pathogens
saliva and tears
contain an enzyme that breaks down bacterial cell walls
gastric secretions
create a highly acidic environment that kills many pathogens that enter the digestive system
internal defence mechanisms
inflammatory response, phagocytosis, natural killer cells, and the complement system
monocyte
a type of white blood cell that circultes the bloodstream and lymph and develops into a macrophage after entering infected tissue
mast cells
take up residence in connective tissues and particularly mucosal tissues
- responsible for releasing chemicals in response to physical injury
- play a role in allergic reactions
cytokine
a chemical messenger that regulates cell differentiation (form and function), proliferation (production), and gene expression to produce a variety of immune responses
- released when a pathogen is recognized as an invader
interferons
a small protein that signals viral infection to other cells
- stimulate uninfected cells to produce compounds that reverse viral replication
- activate macrophages and other cells
inflammation
localized redness, swelling, heat, and pain
- a response to physical trauma, such as a cut or blow, chemical irritation, and infection by pathogens
chemical signals of inflammation
enter the extracellular fluid and cause dilation (expansion) of capillaries and increased permeability of capillary walls
- allows serum and other compounds leaking from capillaries to cause swelling of the area, causing pain
white blood cells inflammatory response
different types of white blood cells are attracted to the area of inflammation depending on the nature of the injury or the infecting pathogens
neutrophil
an early-arriving white blood cell that envelopes and digests pathogens
- most common white blood cells of the immune system
types of phagocytes (eating cells)
- granulocytes
- macrophages
- dendritic cells
granulocytes
eat until they die to protect the body
- large amount of granulocytes
macrophages
slower than granulocytes and must be attracted when there is inflammation
- when unactivated, called a monocyte
- present what they have eaten on the outside of the cell
dendritic cells
located where the inner and outer worlds come into contact, for example in the intestines
- present what they have eaten on the outside of the cell
antigen-presenting cells
such as dendritic cells or macrophages, eat bacteria
lymphocyte
a white blood cell that contains a large nucleus
- most associated with the adaptive immune response, but infected cells are identified and destroyed by natural killer cells, the only lymphocytes of the innate immune system
natural killer cell (NK)
a lymphocyte that can kill cells infected with viruses (or cancer cells)
- identify intracellular infections, especially from viruses, by the altered expression of major histocompatibility I molecules (MHC) on the surface of infected cells
major histocompatibility I molecules (MHC)
proteins on the surfaces of all nuclear cells that sample the internal environment of the cell at any given time
major histocompatibility complex (MHC)
a protein that presents particles of what’s inside the cell, on the outside
- on all cells in the body that show what they have recycled
complement system
a set of about 20 types of proteins activated by infection or the activity of the cells of the adaptive immune system
- aims to destroy extracellular pathogens
- complementary to the innate and adaptive immune systems
complement proteins
bind to the surfaces of microorganisms and are particularly attracted to pathogens that have already been tagged by the adaptive immune system
- serve as a marker to indicate the presence of a pathogen in phagocytic cells and promote acidification
tagging
involves the attachment of specific proteins called antibodies to the pathogen
2 types of adaptive responses
- cell-mediated immune response
- humoral immune response
cell-mediated immune response
controlled by activated T cells
humoral immune response
controlled by activated B cells and antibodies
B cells
are involved in the humoral immune system, which targets pathogens lost in blood and lymph
- stay in the bone marrow to maure
- become immunocompetent
T cells
are involved in the cell-mediated immune response
- migrate to the thymus where they mature
- become immunocompetent
immunocompetent
the cell can recognize a specific molecule or antigen by binding
sensitive B cells
when a B cell encounters the antigen that binds to its receptor, the antigen molecule is taken up into the cell by endocytosis and reappears on the surface of the cell-bound to an MHC class II molecule
- when this process is complete, the B cell is sensitive
helper T cell
in most cases, the sensitized B cell must encounter a helper T cell before a B cell can be activated
- the helper T cell must have already been activated by an encounter with the antigen
B daughter cells
once the helper T cell has reactivated the sensitized B cell, the helper T cell binds to the antigen MHC class II complex and relases cytokines that divide the B cell rapidly, creating plasma cells or memory B cells
memory B cells
remain inactive until a subsequent encounter with the antigen, caused by reinfection by the same bacteria or virus, results in division into a new population of plasma cells
antibody (immunoglobulin (Ig))
a protein produced by plasma cells after stimulation by an antigen
- can be found in the blood, stomach, mucus secretions, and breast milk
antigen-antibody complex
stimulates the complement system and destroys the cell carrying the antigen
antibody neutralization
can occur when pathogens enter and infect host cells
- neutralized antibody-coated pathogens can then be filtered through the spleen and eliminated
opsonization
the process of which antibodies mark pathogens for destruction by phagocytic cells, such as macrophages or neutrophils
complement fixation
some antibodies provide a place for complement proteins to bind
antigen-presenting cell (APC)
detects, engulfs, and informs the adaptive immune response of an infection
helper T lymphocytes (TH)
work indirectly to inform other immune cells of potential pathogens, and divided into TH1 and TH2 cells
- TH1 cells: secrete cytokines to enhance the activities of macrophages and other T cells
- TH2 cells: stimulate naive B cells to secrete antibodies
cytotoxic T lymphocytes (TC)
the major component of the cell-mediated part of the adaptive immune system and attack and destroy infected cells
- particularly important in protecting against viral infections
effector cells
what B plasma cells and TC cells are called collectively
- involved in ‘causing’ the immune response of killing pathogens and infected host cells
memory cell
an antigen-specific B- or T-lymphocyte that does not differentiate into an effector cell during the primary immune response, but can immediately become an effector cell upon re-exposure to the same pathogen
- persist in the bloodstream
secondary immune response
if the host is re-exposed to the same pathogen type, circulating memory cells will immediately differentiate into plasma cells and TC cells without input from APCs or TH cells
lymph
the watery fluid that bathes tissues and organs and contains protective white blood cells, but not erythrocytes
- moves around the body through the lymphatic system, consisting of blood vessels, lymph vessles, lymph nodes, and organs such as tonsils, adenoids, thymus, and spleen
extravasation
the process of which cells of the immune system can move between the various lymphatic and blood circulatory systems, which are separated by interstitial space
immune tolerance
the acquired ability to avoid an unnecessary or harmful immune response to a detected foreign substance known not to cause disease or self-antigens
- established by specialized APCs in the liver, lymph nodes, small intestine, and lungs that present harmless antigens to a diverse population of regulatory T cells (Treg cells), specialized lymphocytes that suppress local inflammation and inhibit the secretion of stimulatory immune factors
combined result of Treg cells
to prevent immunological activation and inflammation in unwanted tissue compartments and to allow the immune system to focus on pathogens instead
HIV
infects T helper cells using their CD4 surface molecules, gradully depleting the number of T helper cells in the body
- inhibits the adaptive immune system’s ability to generate sufficient responses to infections or tumours
immunodeficiency
a failure, insufficiency, or delay in the response of the immune system, which can be acquired or inherited
- can allow for pathogens or tumour cells to gain a foothold and replicate or multiply to a high enough level that the immune system becomes overwhelmed
- can be acquired as a result of infection with certain pathogens that attack the cells of the immune system itself, chemical exposure, malnutrition, or extreme stress
hypersensitivity
an inappropriate immune response to harmless foreign substances or self-antigens that occurs after sensitization of the tissue
allergies
a form of hypersensitivity
- upon initial exposure to a potential allergen, an allergic individual produces antibodies by the typical process of APCs, which present antigents to T helper cells that stimulate B cells to produce the antibodies
- the antibody molecules interact with mast cells, embedded in connective tissues
- this process stimulates or sensitizes the tissue
anaphylactic shock
on subsequent exposure to the same allergen, the antibody molecules on mast cells bind the antigen and stimulate the mast cells to release histamine and other inflammatory chemicals that causes the sympoms of allergy
- antihistamines not enough to counteract anaphylactic shock
- epinephrine (EpiPen) used to counteract the blood pressure and respiratory effects
autoimmunity
a form of hypersensitivity to self-antigens that affects approximately 5% of the population
autoantibody
an antibody that mistakenly marks self-components as foreign
