Host Defenses Flashcards
Pathogen
Any organism that can cause disease
Two types of defenses
Innate immunity and Acquired immunity
Innate Immunity property
Innate immunity is non-specific, it doesn’t distinguish one pathogen from another. Rapid response
Acquired (adaptive) immunity
Immune system, specific, and diverse. Slow response
Unwanted intruders
viruses, bacteria, abnormal cells
Two types of innate immunity
External and internal
First line of defense
External innate immunity
3 components of external innate immunity
Skin, mucous membrane, chemicals
The Skin
physical barrier, pathogens cannot penetrate. Part of external innate immunity.
Mucous Membrane
Lines digestive, respiratory, and genitourinary tracts. It is a physical barrier and the mucous membrane produces mucus.
Mucus
Traps microbes and other particles. Produced by mucous membrane.
2 types of chemicals of external innate immunity
- Sweat glands
2. Saliva, tears, and mucous excretions
Sweat glands
Sweat glands excrete acids which inhibit bacterial growth.
Saliva, tears, and mucous excretions
They wash away pathogens. They also contain lysozyme, which destroys bacterial cell walls.
Inner Innate Immunity
Second line of defence»_space;> Inflammatory Response
Inflammatory response occurs when
Tissue is damaged (injury) and/or microorganisms enter (infection)
First step of inflammatory response
Damaged cells and microorganisms release chemical signals, including histamines, prostaglandins, and chemokines.
What does the release of chemical signals by the damaged cells and microorganisms do?
This causes capillary dilation, which increases permeability and blood flow to the injury site. This results in swelling, redness, and heat.
Increased permeability and blood flow to the injury site allows for what?
Allows clotting factors and phagocytic cells to get to the injury site.
Three chemical signals for inflammatory response
Histamines, Prostaglandins, and chemokines
What releases histamines?
Circulating basophils and mast cells (tissue basophils)
Prostaglandins are released by what?
White blood cells and damaged tissue
Chemokines
Proteins. Small cytokines. They are released by blood vessels and monocytes (type of white blood cell). They attract phagocytic cells like traffic cops.
Second step of inflammatory response
Phagocytosis
Phagocytosis
White blood cells ingest invading microbes.
Three types of cells involved in phagocytosis
Neutrophils, Macrophages, and Dendritic Cells
Neutrophils
Cell involved in phagocytosis. Neutrophils are first at the site. They engulf the microbe and self-destruct (suicidal). Consequently, they are short-lived.
Macrophages
Macrophages are long-lived large eaters. They eat more than neutrophils (stronger response). They also clean up damaged tissue and cells.
How Macrophages are made
Monocytes (type of white blood cell) migrate to the tissues where they develop into macrophages.
Dendritic Cells are very important where?
Dendritic cells are very important in the immune system.
Which type(s) of cells present antigens to T-Cells?
Macrophages, and Dendritic Cells
Dendritic Cells
Dendritic cells present antigens to T-Cells (t-Lymphocytes), starting the immune system.
Antimicrobial proteins
Also get to injury site due to capillary dilation and is a part of inflammatory response in inner innate immunity.
Two types of antimicrobial proteins
Complement and Interferon
Complement system
Made up of 30 serum proteins. Proteins are inactive in the absence of a pathogen. Pathogen causes complement 1 to become active (30 of these processes) - cascade. Final protein causes lysis of the cell that interacted with it. (pathogen)
Function of Cytokines
Protect against disease. Peptide Alarm bells
Interferons
Interferons are a type of cytokines. Virus infected cells release interferons and cells next to it respond to them. Inhibits viral reproduction and Interferons are non-specific (any virus) and short-lived.
Non-phagocytic cells
They don’t eat pathogens
Non-phagocytic cells involved in inflammatory reponse
Eosinophils and Natural Killer cells (NK)
Eosinophils
Type of white blood cell. Eosinophils discharge digestive enzymes on the wall of parasites.
Natural Killer Cells (NK)
NK cells attach to cell membrane of virus-infected cells and some cancer cells, causing cell death.
How to differentiate between cancer and normal cells
Cancer and normal cells have small differences in proteins
What does it mean when we call Adaptive (acquired) immunity diverse?
It responds to numerous types of invaders.
The Cells involved in adaptive immunity
Lymphocytes
Two types of lymphocytes
T and B
Origin of lymphocytes
Both T and B lymphocytes (all of them) develop from same stem cell in bone marrow.
B-Cells
B-Cells mature in the bone marrow (hence the b). B cells produce antibodies and are involved in the humoral immune response.
T-Cells
T cells mature in the thymus. T-cells are involved in cell mediated immune response.
Antigen
Foreign protein or long polysaccharide. Antigens by definition activate (elicit a response from) lymphocytes. Antigens have unique structures.
Antigens found on the surface of, produced by or release from:
Viruses, Bacteria, Fungi, Parasites, Protozoa, Pollen, and Transplanted Tissue
B Cell Antigen Receptors
One B Cell has thousands of antigen receptors that are all identical (for one Antigen). Has a Y-Shaped antigen receptors (polypeptide).
Y shaped polypeptide
4 polypeptide chains. 2 identical heavy chains and 2 identical light chains, linked together by disulfide bridge. Similar in structure to antibodies
T Cell antigen receptors
Like B Cells, a T cell has thousands of all identical antigen receptors (for ONE antigen). T Cell Antigen receptors are not Y shaped. They are formed with two polypeptide chains held together by a disulfide bridge. T cell antigen receptors recognize antigen fragments expressed on the surface of cells.
MHC
Major Histocompatibility Complexes are glycoproteins embedded in the cell surface. They express antigen fragments.
MHC Functions
Presentation of antigens (fragments) to T-Cells. Immune tolerance to self.
Failure of MHC could lead to…
Autoimmune diseases (lack of immune tolerance to self - one of the functions of MHC).
MHC 1
MHC 1 found in most nucleated cells. Antigen fragments that are expressed on the surface are recognized by Cytotoxic T Cells.
MHC 2
Found in antigen presenting cells (Dendritic cells, macrophages, B-cells)»_space;> all nucleated, but they are the exception.
Antigen fragments expressed on the surfaces (while attached to MHC) are recognized by Helper T Cells.
2 classes of MHC
MHC 1 and MHC 2
Why is it unlikely that 2 individuals have the same set of MHCs?
20 genes code for MHC. Each gene has numerous alleles (alternatives)
First step of presenting antigens to T-cells
Invader has been internalized. Antigen is degraded.
Second step of presenting antigens to T-cells
At the same time as step 1, MHC are produced. Antigen fragments bind to (is processed by) MHC.
Final step of presenting antigens to T-cells
Antigen fragment and MHC are expressed on the surface of the cell, and they interact with T cells (helper and cytotoxic)
Two types of T-Cells
Cytotoxic and Helper T Cells
Cytotoxic T cell
React with cells expressing MHC I + Antigen. They kill the infected cell.
Helper T Cell
React with cells expressing MHC II + antigen (antigen presenting cells like dendritic cells, macrophages, and b-cells). They stimulate other cells.
Antibodies
Antigen-binding immunoglobulin (protein)
Antibodies recognize…
an epitope
Epitope
Region of an antigen that an antibody recognizes.
Antibodies are secreted by…
Activated B Cells.
Activated B cells alternative name
Plasma Cells
Antibody Structure
The same as the Y shaped antigen receptors on B-cells, excluding the transmembrane region.
All polypeptide chains of antigen receptors composed of
A variable region and a constant region.q
Variable region
Amino acid sequence varies from antibody to antibody. Involved in the binding of the antibody to the antigen, which resembles enzyme-substrate interaction.
Constant region
Important for antigen disposal.
3 ways antibody disposes antigen
Neutralization, Opsonization, Complement Fixation
Neutralization
Antibodies attach onto antigens on the surface of a virus and prevent viral attachment. The virus therefore cannot infect cells.
How do antibodies kill pathogens?
They don’t, they facilitate their destruction.
Opsonization
Antibodies bind to antigens on bacterial surface, which enhances phagocytosis (makes it easier)
Complement Fixation
Antibodies bind to antigen on surface of pathogen. Complement links two adjacent bound antibodies. Complement becomes activated (cascade). Complement attaches onto pathogen membrane, forming a pore. Fluids rush in leading to cell lysis.
Response to the entrance of an antigen (term)
Clonal selection
What does the specificity of a lymphocyte mean?
Which particular type of antigen activates the lymphocyte
When is the specificity of lymphocytes determined?
The specificity of lymphocytes is determined during embryogenesis. i.e. before antigens are encountered.
When does clonal selection occur?
When lymphocytes recognize an antigen.
First step of clonal selection
Antigen enters the body and binds to a corresponding lymphocyte (the variable region of its antigen receptors).
Second step of clonal selection
Lymphocyte is activated and mitosis occurs, producing thousands of identical clones that are specific for and dedicated to eliminating the activating antigen.
Final step of clonal selection
Clones develop into either effector cells or memory cells.
Effector Cells
Active. They are short-lived and they destroy activating antigens.
Memory Cells
Inactive. They are long-lived and they bear receptors for the activating antigen. When they are activated, they can give rise to effector cells.
Effector form(s) of T Cells
Helper and Cytotoxic T cells
Effector form(s) of B cells
Plasma Cells
When does the primary immune response occur?
Body’s first exposure to an antigen
When does the secondary immune response occur?
Body’s exposure to a previously encountered antigen.
Primary immune response process and speed
Clonal selection of B and T cells results in effector and memory cells. The Primary immune response peaks 10-17 days after exposure.
Secondary immune response process and speed
Memory cells are activated, and they produce many more effector cells than the primary immune response, thus it is a stronger response. The Secondary immune response peaks 2-7 days after exposure. Thus it is faster than the primary immune response.
Two pathways of Adaptive (Acquired) Immunity
Humoral and Cell-mediated immunity pathways.
Humoral immunity pathway broadly involves what? What activates it and what does it do?
Involves B Cell activation. Free antigens can activate this pathway. Produces Antibodies.
Intracellular definition
Inside the cell
Cell mediated immunity pathway involves…
It involves T Cell activation by intracellular antigens, fungi, protozoa, parasitic worms, transplanted tissue, and cancer cells.
How are the humoral and cell-mediated immunity pathways linked?
They are linked by Helper T cells, which alert the immune system.
integral membrane protein definition
Protein that is located within the membrane
Cell-mediated pathway first path involving professional antigen presenting cell - first step
dendritic cell or macrophage engulfs invader and antigen is expressed on its surface using MHC II
Second step of professional antigen presenting cell in cell mediated immunity pathway
helper T-cell interacts with MHC II and antigen fragment. This is facilitated by CD4 in helper T cells
CD4
integral membrane protein found in helper T Cells
Another name for Helper T Cells
CD4 Cells
Third step of professional antigen presenting cells in cell mediated pathway
Clonal selection, resulting in effector cells (active) and memory cells. Effector cells secrete cytokines known as interleukin 2 (IL2) which activates B cells and cytotoxic cells.
How are helper T cells regulated?
Helper T Cells are regulated by cytokines. IL1 released by macrophages and IL2 feedback activation (positive control).
Other name for cytotoxic cells
CD8 Cells
Infected cell path for cell mediated immunity pathway steps
Infected cell binds to cytotoxic cell, which is enhanced by CD8 integral membrane protein. Cytotoxic cell becomes activated (effector cell), and it releases perforin (complement). The complement forms pores in the membrane of the infected cell, causing cell lysis.
Why is infected cell lysis good in the cell mediated immunity pathway?
It exposes the pathogen to antibodies and destroys the pathogen’s site of reproduction.
2 paths of cell-mediated immunity pathway
- Professional Antigen Presenting cell (APC) engulfs invader
- Infected cell expresses antigen fragment on its surface
Humoral definition
Antibody-mediated
Professional Antigen presenting cells
Macrophages, Dendritic Cells, B Cells - these can be just called antigen presenting cells, for the purposes of our biology level.
Plasma Cell
Effector B Cell, produces antibodies.
Humoral immunity pathway steps
- Antigen binds to B-cell receptor. B-cell expresses antigen on its surface using MHC II.
- At the same time, an antigen presenting cell engulfs an antigen and expresses a fragment of it using MHC II. A helper T-cell interacts with this fragment with the help of CD4 integral membrane protein. This activates the Helper T-cell
- Finally, the activated helper t-cell and B-cell produce 2 clones: Effector cells (plasma cells) which produce antibodies and memory B cells.
How can immunity be achieved?
Immunity can be achieved naturally or artificially.
Immunization
Achieving Immunity
2 types of immunization
Active and Passive
Active immunization
Conferred by recovery from an infectious disease. Depends on the individual’s own immune system. May be acquired from natural infection or artificially through vaccination.
Vaccine Components and Effects
A vaccine is an inactivated toxin made up of dead microbes. Only the parts of microbes are necessary to make a vaccine. Won’t cause disease as it acts only as an antigen. Vaccinated individuals show a rapid memory based response.
Passive Immunization
Transferring antibodies from one individual to another.
Natural Passive immunization examples
Mother to fetus (antibodies can cross the placenta). Mother to infant (nursing (breastfeeding) provides temporary protection for a few weeks to months until infant develops immune system).
Artificial Passive immunization process and example
Inject antibodies into an individual. For example rabies antibodies.
Categories of immune diseases
There are 3: Allergies, auto-immune, and immunodeficiency.
Allergies
Hypersensitivity of the immune system to an allergen.
Allergy process steps
Allergen causes an immune response. Antibodies produced by the immune system bind to mast cells in connective tissue. Allergen binds to this antibody-mast cell, causing it to release histamine and therefore triggering an inflammatory response.
Autoimmune diseases
Immune system acts against the self
Examples of autoimmune diseases
Rheumatoid arthritis, Multiple Sclerosis, Lupus, and Diabetes
Rheumatoid arthritis
Inflammation of joints due to autoantibodies. A type of autoimmune disease.
Multiple Sclerosis
T cells attack Myelin Sheath. Autoimmune disease
Lupus
Autoantibodies attack histones, DNA. Autoimmune disease
Diabetes
Cytotoxic cells attack the cells of the pancreas. Autoimmune Disease
Examples of immunodeficiency diseases
Severe Combined Immunodeficiency (SCID), Hodgkin’s Disease, Physical and Emotional Stress, Acquired immunodeficiency syndrome (AIDS)
SCID
Severe combined immunodeficiency is inborn. Both limbs of the immune system do not function. Must live in a bubble.
Hodgkin’s Disease
Type of cancer that damages the lymphatic system. Immunodeficiency disease
Physical and Emotional stress
Hormones released by stressed individuals reduce white blood cell count.
Immune-nervous system links
Lymphocytes have receptors for neurotransmitters.
AIDS
Acquired immunodeficiency Syndrome is caused by HIV. Glycoproteins on the surface of the virus bind to CD4 integral membrane proteins of the Helper T cell, reducing their numbers.
