Immune system Flashcards
Assaults on the body
- external: microorganisms, protozoans, bacteria, and viruses
- internal: include abnormal cells that reproduce and form tumors that may become cancerous and spread
Immune system organization
- Antigens
- Self vs no self
- Innate immunity / non specific
- Adaptive immunity / specific
QAntigens
q- a protein marker on the surface of cells to identify them
- stimulate the production of antibodies
- immunocompetence: the ability to activate an effective response to a foreign antigen
Self markers
Molecules on the surface of human cells that are unique to an individual, thus identifying the cells as self to the immune system
- MHC: major histocompatibility complex
Non-self markers
Molecules on the surface of foreign or abnormal cells or particles that identify the particle as “non-self” to the immune system
Self-tolerance
The ability of our immune system to attack abnormal or foreign cells, but spare our own normal cells
Innate immunity / nonspecific
Present at birth
- built in and ready for action providing the initial defense mechanism
Adaptive immunity / specific
Mechanisms that develop in response to specific threatening agents or specific abnormal cells
Cytokines
Broad and loose category of small proteins that are important in cell signaling
- they are released by cells and affect the behavior of their cells or the cells that release them
- regulate or initiate innate and adaptive immunity
- ex: interleukins, leukotrienes, and interferons, growth factors
Pic
Pic
Innate immunity: mechanical and chemical barriers
First line of defense is the skin and mucous membranes
- sebum, mucus, enzymes, and hydrophobic acid in the stomach
Innate immunity: inflammatory response
Provides a second line of defense
- tissue damage - release of inflammation mediators (histamine, kinins, prostaglandins, leukotrienes, and interleukins)
- many of these mediators are chemotactic factors: substances that attract WBCs to area (chemotaxis)
Innate immunity: inflammation
Due to increased blood flow and vascular permeability in the affected region, which help phagocytosis WBCs reac the general area and enter the affected tissue
- redness - warmth - pain - edema
Pic
Pic
Innate immunity: phagocytosis
- a major component of second line of defense (but also plays role in adaptive immunity)
- the ingestion and destruction of microorganisms or their small particles by phagocytes
- cells that perform this funciton are called antigen-presenting cells
APC
Antigen-presenting cells
- phagocytes that ingest foreign particles, isolate protein segments (peptides), and display them as antigens on their surfaces
- these peptides are then recognized by cells of the adaptive immune response by a specific (adaptive) immune cell
Neutrophils
Most numerous; first responder
Macrophages
Large eaters
- phagocytes monocytes that have grown to several times their original size after migrating out of the blood stream
Dendritic cells
Cells with many extensions
- found in many body tissues that are in contact with the external environment, such as the skin and mucous membranes
Innate immunity: natural killer cells
- lymphocytes (not T or B) that kill tumor cells and cells infected by viruses
- chemically triggers cell death and destruction
- must have direct contract with target cell
- NK cell recognize abnormal cells by using two different recognition receptors (killer-activating and killer-inhibiting receptor)
Killer-activating cells
Binds to any of several common surface molecules found in cells
Killer-inhibiting cells
If the NK cell also binds to protein found on the surface of normal cells, then the killing action is stopped
- only abnormal and foreign cells fail to bind to the killer-inhibiting centers, so they are destroyed
Pic
Pic
Innate immunity: Interferon
IFN
- a protein synthesized by lymphocytes, macrophages, and fibroblasts that have been invaded by viruses
- interferon diffuses into the circulation and to nearby cells
- interferon proteins interfere with the ability of viruses to cause disease by preventing replication
Innate immunity: Complement
A group of enzymes that produce a cascade of reactions resulting in a variety of immune responses
- lyes cells when activated by either adaptive or innate mechanism
- enhances inflammation and phagocytosis
Pic
Pic
Innate immunity: Toll-like receptors
In the membranes of the host cells
- they are pattern-recognition receptors
- they do not identify specific antigens
- they identify a large variety of different bacterial molecules such as toxins and flagell proteins, viral RNA and glycoproteins, and fungal molecules
- when triggered, they facilitate the nonspecific/innate immune mechanisms
Adaptive immunity
Third line of defense
- these mechanisms attach specific agents that the body recognizes as abnormal or non-self
- consists of two different classes of lymphocytes (B and T cells)
Pic
Pic
Adaptive immunity: Lymphocytes
Adaptive immunity requires activation of lymphocytes populations, which then begin their immune attack of specific antigens
- each lymphocyte has receptors for both an antigen and for signaling chemicals
- requires two stimuli
1. A specific antigen
2. Activating chemicals
B lymphocytes
B cells
- do not attack pathogens themselves by instead produce molecules called antibodies that attack the pathogens
- B cell mechanisms are classified as antibody-mediated immunity or humoral-mediated immunity
Activation of B cells
Develop in two stages
- pre B cells (naive cells) develop by a few months of age
- the second stage occurs in lymph nodes and spleen with activation of a naive B cell after it binds to a specific antigen
- activated B cells become antibody-secreting plasma cells (effector B cells)
- inactive B cells are Memory B cells
- when exposed to the antigen that triggered their formation, they rapidly prude more plasma cells and memory cells
Pic
Pic
Functions of antibodies
The function of antibody molecules is to produce antibody-mediated immunity (humoral immunity) by disabling antigens
- antigen-antibody reactions
- complement activation
- primary and secondary responses
Antigen antibody reactions
The binding of the antigen to antibody forms an antigen-antibody complex that may produce one or more effects
- transforms toxins into harmless substance
- clumps antigens together (agglutination), making it possible for macrophages to dispose of them more rapidly
T lymphocytes
T cells
- attack pathogens more directly
- T cell mechanisms are classified as cell- mediated immunity or cellular immunity
Function of T cells
- T cells funciton to produce cell-mediated immunity and help to regulate adaptive immunity in general
1. Helper T cells
2. Cytotoxic T cells
3. Suppressor T cells
4. Memory T cells
Helper T cells
Regulate the function of B cells, T cels, phagocytes, and other WBCs
Cytotoxic T cells
An effector T cell that causes contact killing of a target cell
Suppressor T cells
Regulatory T cells that suppress lymphocyte fucntion, thus regulating immunity and promoting self-tolerance
Memory T cells
Inactive T cells that stay in the circulation
- if the same antigen entes the body again, these cells can be activated and proliferate to respond to the antigen quickly
Pic
Pic
Adaptive complement
- a component of blood plasma consisting of several protein compounds
- complement kills foreign cells by cytolysis or apoptosis
- complement causes vasodilation, enhances phagocytosis, and other functions
- complement activity can also be initiated by innate immune mechanisms
Primary response
Initial encounter with a specific antigen triggers the formation and release of specific antibodies that reaches its peak in a few days
Secondary response
A later encounter with the same antigen triggers a much quicker response
- B memory cells rapidly divide, producing more plasma cells and thus more antibodies
Adaptive immunity review
Adaptive immunity is a specific immunity targeting specific antigens
- adaptive immunity involves two classes of lymphocyte: B and T cells
- B cells: antibody-mediated (humoral) immunity
- T cells: cell-mediated (cellular) immunity
Adaptive immunity types
- Natural immunity: results form non-deliberate exposure to antigens
- occurs in the course of everyday living - Artificial immunity: results from deliberate exposure to antigens, called immunization
Immunity
Natural and artificial immunity may be active or passive
- Active immunity: when the immune system responds to a harmful agent; lasts longer than passive
- Passive immunity: developed when immunity from another individual is transferred to an individual who was not previously immune; it is temporary but provides immediate protection
