Immune System Flashcards
Innate & Adaptive Immunity
Invertebrates have only innate immunity
Vertebrates have innate and adaptive immunity
Innate defense
refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen’s appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and cells that attack foreign cells in the body.
Adaptive (acquired) defense
refers to specific defense mechanisms that involve cells (lymphocytes) and proteins. Some of these cells have “memory”. This is the technical use of the term “immunity”.
Innate defenses
first and second lines of defense
Found in all animals
-First Line includes both mechanical and chemical
-Skin with secretions of sebaceous (oil) glands
-Mucous membranes
-Ciliary escalator of respiratory system
-HCl of stomach
Second Line includes both cells, proteins, and “processes”
-Cells = macrophages and natural killer (NK) cells
-Proteins = complement and interferon
-Processes = fever and inflammation
Macrophages
2nd line of defense
“big eaters”
Digest foreign substances (toxins and microbes) in a non-specific way
Represent the primary antigen presenting cells (APC’s)
• present foreign substances to lymphocytes of 3rd line
of defense (…..more later)
NK Cells
Second line of defense
technically, these are a type of lymphocyte
- Primarily involved with killing cancer cells
Complement proteins
“complement” both the non-specific as well as the “specific” -
The complement system consists of a number of small proteins in the blood, in general synthesized by the liver, and normally circulating as inactive precursors.
When stimulated by one of several triggers, proteases in the system cleave specific complement proteins and initiate an amplifying cascade of further cleavages.
The end-result of this activation cascade is massive amplification of the response and activation of the cell-killing membrane attack complex
Interferons
Second line of defense
proteins produced by virus-infected cells
Interferons help other cells resist viruses
Inhibit viral replication
Found only in vertebrates
The inflammatory response can
Disinfect tissues Dilute toxins Limit further infection (trap microbes) Recruits phagocytes Promotes healing
Four Cardinal Signs of Inflammation
Swelling
Redness
Heat
Pain
Tissue damage
triggers the inflammatory response Damaged cells release histamine Histamine leads to vasodilation Dilated vessels become more leaky (increased vascular permeability) Various WBC’s migrate out into tissue
FEVER
- is defined as having a temperature above the normal range due to an increase in the body’s temperature set-point.
- interleukin-1(IL-1) from macrophages targets the hypothalamus in the brain and re-sets the set-point and acts as a pyrogen
The lymphatic system
is a network of -Lymphatic vessels -Organs Lymphatic vessels -Collect fluid from body tissues -Return it as lymph to the blood Lymph organs -Such as the spleen and lymph nodes -Are packed with white blood cells that fight infections
As lymph circulates through lymphatic organs it
Collects
-Microbes
-Microbe toxins
Transports them to lymphatic organs
-Macrophages in lymphatic organs engulf the invaders
-Lymphocytes mount acquired immune response
Our immune system
Responds to foreign molecules called antigens The acquired immune system -Reacts (adapts) to antigens -…….And “remembers” an invader. -The immune system has “memory”.
Active & Passive Immunity
Infection or vaccination triggers active immunity
We can temporarily acquire passive immunity by receiving pre-made antibodies
Immunity can also be natural or artificial
Two kinds of lymphocytes carry carry out the immune response
B cells -Secrete antibodies -Mount the humoral immune response -Best against bacteria T cells -Attack cells infected with viruses -Cell-mediated immune response
Millions of kinds of B cells and T cells
Each with different membrane receptors
Wait in the lymphatic system
Where they may respond to invaders
Antigens
Not usually part of the host
Most are proteins or large polysaccharides on the surfaces of
-Viruses
-Foreign cells
Antigenic determinants
Specific regions on an antigen
To which antibodies bind
When an antigen enters the body
It activates only a small subset of lymphocytes
-Those with complementary receptors
The selected lymphocyte cells multiply into clones of short-lived effector cells
-Specialized for defending against the antigen that triggered the response
-And into memory cells that confer long-term immunity
he steps of clonal selection
Primary immune response, clonal selection
-Occurs upon first exposure to an antigen
-Is slower than the secondary immune response
-Produces effector cells…..and……
-Memory cells that may confer lifelong immunity
Secondary immune response
-Memory cells are activated by a second exposure to the same antigen
-This initiates a faster and stronger response
Antibodies
Are secreted by plasma (effector) B cells Into the blood and lymph An antibody molecule -Is Y-shaped -With two antigen-binding sites -Specific to the antigenic determinants -That elicited its secretion
Antibodies promote antigen elimination through several mechanisms
Mark invaders ……neutralization
agglutination
precipitation
Which triggers mechanisms to neutralize or destroy invaders…….opsinozation (enhanced phagocytosis)
Activate complement system…..fix complement
T-Cells
Regulatory
- Helper T cells………….up-regulate
- Suppressor T-cells…..down-regulate
Effector
- Cytotoxic T cells (aka “killer T-Cells”)
- Are primarily responsible for the cell-mediated immune response
In the cell-mediated immune response, an antigen-presenting cell (APC) displays
A foreign antigen (a nonself molecule) and
One of the body’s own self proteins
To a helper T cell
Major Histocompatability Complex
“Self Antigens” = MHC antigens MHC Antigens = Major Histocompatability Complex MHC I = on all of the cells of the body MHC II= only on APC’s
The helper T cell
The helper T cell’s receptors -Recognize the self–nonself complexes -The interaction activates the helper T cells The helper T cell can then activate -Cytotoxic T cells and B cells
Cytokines
Cytokines = cellular hormones = Biochemical Mediators of the Immune Response
- Interleukin-1…….from macrophages - activates Th-Cells - also acts as a pyrogen - Interleukin-2…….from Th-Cell - activates B-cells and Tc-Cells - activates other Th-Cellsand re-activates itself
Cytotoxic T cells
Cytotoxic T cells -Are the only T cells that kill infected cells Cytotoxic T cells -Bind to infected body cells -Destroys them -Inserts perforin proteins into membrane
The immune system normally reacts
Only against nonself substances
Not against self
Transplanted organs
May be rejected
Because the transplanted cells lack the unique “fingerprint” of the patient’s self proteins
Donors are used that most closely match the patients tissues
Transplants between identical twins do not typically have this problem
In autoimmune diseases
The immune system turns against the body’s own molecules Examples include -Lupus -Rheumatoid arthritis -Insulin-dependent diabetes mellitus -Multiple sclerosis
