Unit 6 Flashcards
Immunity
The ability of the body to fight off invaders/pathogens.
Primary Lymphoid Organ
Organs where lymphocytes develop. Bone marrow and thymus.
Secondary Lymphoid Organ
Where lymphocytes interact and initiate responses. Spleen, lymph nodes, tonsils, and Gut Associated Lymphoid Tissue (GALT). Filters blood and lymph for pathogens and pathogen containing lymphocytes. Pulp inside allows mixing of lymphocytes and other leukocytes. Arteries and veins supply nutrients and O2.
Lymph
A clear fluid where active immune cells are found.
Lymph Vessel
Carry lymph and are attached to lymphoid organs.
Eosinophils
Cytotoxic granulocytes with bright pink staining granules. Role in defence against parasites and function in allergic response. Few in peripheral circulation (only live 6-12 hours). Found in digestive tract, lungs, genital tract, and skin. Respond by binding to an antibody-coated parasite and degranulate. Granule contents (toxic enzymes and oxidative chemicals) damage and kill parasites. Can also degranulate in allergic responses.
Basophils/Mast Cells
Granulocytes involved in allergic responses. Have large dark blue staining granules. Basophils are found in the blood while mast cells are found in tissues such as the digestive tract, lungs, and skin. Granules contain histamine, heparin, and cytokines.
Neutrophils
Granulocytes that are phagocytic. Are the most abundant leukocyte (50-70% of total leukocytes). Live 1-2 days and can ingest 5-20 bacteria. Can leave the circulatory system to attack pathogens in tissues. Granules contain cytokines that cause fever and start other inflammatory responses.
Monocytes
Are precursor cells of tissue macrophages and are uncommon in blood (1-6% of leukocytes). Estimated in the blood for 8 hours before moving into tissues to become macrophages.
Lymphocytes
Key players in the adaptive immune response. Make up 20-30% of all leukocytes. Only 5% of them are in circulation (most are found in lymphoid tissues). 10^12 per individual at any given time. They all look alike under a microscope but have fundamental differences in function.
Dendritic Cells
Phagocytic antigen presenting cells (APCs). Have long thin processes (like dendrites on a neuron). Found in skin and other organs. They recognize and engulf pathogens to place on cell surface. Activated cells migrate to secondary lymphoid organs to present the antigens to lymphocytes.
Granulocytes
Have prominent cytoplasmic granules. Eosinophils, basophils (mast cells), and neutrophils.
Phagocytes
Can engulf and ingest pathogens. Neutrophils, macrophages (monocytes), and dendritic cells.
Cytotoxic Cells
Kill other cells and even self-cells. Eosinophils and some lymphocytes (cytotoxic T cells and natural killer cells).
Antigen Presenting Cells (APCs)
Display fragments of pathogens on cell surface. Some lymphocytes (certain B cells), dendritic cells, and macrophages.
Innate Immunity
Present before pathogen is encountered and is non-specific. All organisms have this.
Adaptive Immunity
Directed at specific invaders and develops after the pathogen is encountered. It remembers past infections. Is broken down into cell-mediated immunity and antibody-mediated immunity (humoral immunity). Only found in vertebrates.
Humoral Immunity
Antibody-mediated immunity due to B cells.
Cell-Mediated Immunity
Relies on cells, not antibodies.
Chemotaxin
Attract leukocytes to the infected area.
Cytokines
Chemicals that affect growth or activity of other cells.
Interleukins
A group of cytokines that play a role in cell-to-cell communication and regulating immune response.
Complement
A collective term for over 25 blood proteins.
Phagocytosis
Eating particles such as bacteria or other pathogens.
Opsonin
The protein that is used to mark a pathogen for destruction. Often found in the blood.
Natural Killer Cells (NK)
Are lymphocytes associated with both innate and adaptive immunity. Act within minutes and do not have specific receptors. They bring about apoptosis (programmed cell death) in pathogen-infected cells. Can also attack tumour cells. They produce important cytokines such as interferons.
B Lymphocytes/Cells
Are produced in the bone marrow and produce antibodies either on cell surface or secrete them into the plasma.
Plasma Cells
Activated B cells that produce antibodies. Are short lived and die after the response is over. Very few live on as memory cells.
Cytotoxic/Killer T Cell (Tc)
Recognize antigens represented on Class I MHC. Kills cell that expresses appropriate antigen.
Helper T Cell (TH)
Recognize antigens on Class II MHC. Promote differentiation of B cells and Tc cells and can activate macrophages.
Regulatory T Cell (Tregs)
Recognize antigens presented on Class II MHC. Suppress other immune cells to prevent excessive immune responses.
Antigen (Ag)
Substances that are recognized by an antibody and induces an immune response (foreign substance).
Immunoglobulin/Antibody (Ab)
Proteins that bind specifically to antigens and target pathogens for destruction. Are most effective against extracellular pathogens (before they invade a cell).
Neutralization
Preventing a pathogen from entering a cell.
T Cell Receptor
Detects antigens presented on the surface of a target cell (cannot bind free antigen).
Major Histocompatibility Complex Receptor
Displays antigens on the cell’s surface for cells to recognize.
MHC Class I
On all nucleated cells. Display for cytotoxic T cells which kill the cell by releasing perforin, granzymes, and releasing the Fas ligand.
MHC Class II
On antigen-presenting cells. Cells respond to extracellular pathogens by phagocytosing said pathogens and displaying for helper T cells or regulatory T cells. Helper T cells secrete cytokines that activate other immune system cells while regulatory T cells secrete cytokines that suppress other immune system cells.
Haematopoiesis
All blood cells are produced in the bone marrow and are derived from pluripotent haematopoietic stem cells which give rise to uncommitted stem cells. These give rise to committed progenitor cells which develop into each cell type. The path taken is guided by cytokines.
Complement Activation
Three pathways.
Extracellular Bacteria Response
1) Complement proteins are activated by bacterial cell wall components.
—> Some act as chemotaxins and attract leukocytes from circulation.
—> Some form MAC Attack and lyse bacteria.
—> Some opsonize bacteria helping phagocytes digest encapsulated ones.
2) Haemostasis occurs if a blood vessel is broken.
3) Phagocytes produce cytokines and the activated lymphocytes present antigens.
4) Cytokines secreted by helper T cells activate B cells.
5) B cells clonally expand becoming plasma cells that produce antibodies that act as opsonins and/or activate complement.
6) End of response, most lymphocytes die but some become memory cells.
Intracellular Viral Response
1) Infected host cell produces IFN β and macrophages produce IFN α which induces an antiviral state in nearby cells.
2) Cytokines are secreted from host cells and macrophages activate NK and cytotoxic T cells.
3) Cytotoxic T cells recognize MHC Class I and kill the infected cell.
4) Some viruses turn off MHC Class I expression on the infected host cell. NK cells kill any cell with no MHC Class I on its surface.
5) End of response, most cytotoxic T cells die but some become memory cells.
Allergic Response
1) Sensitization Phase
—> Equivalent to primary immune response.
—> Antigen is ingested by antigen presenting cell which activates helper T cells.
—> Helper T cells activate B cells to make IgE antibody class.
—> Helper T cells and B cells become memory cells.
2) Re-Exposure
—> Equivalent to a secondary response (body reacts strongly and rapidly).
—> Generally, IgE on mast cells detect the allergen.
—> Mast cells degranulate releasing cytokines and histamines resulting in an inflammatory reaction.
Key Features of the Immune System
1) Lymphoid Tissues
2) Immune Cells
3) Chemicals That Coordinate and Execute Immune Function
3 Major Functions of the Immune System
1) Protecting the body.
2) Removing dead/damaged tissue and cells.
3) Trying to recognize and remove abnormal cells.
Autoimmune Disease
When the immune system targets the own body (incorrect responses).
Allergies
When the immune system overreacts (overactive responses). Are an inflammatory immune response to a non-pathogenic antigen.
Immunodeficiency
When the immune system does not react (lack of response).
Pathogens
Disease-causing agents.
Bacteria
Cells surrounded by a cell membrane and usually a cell wall. Can be intra or extracellular invaders. Can survive and reproduce outside of host. Most can be killed by drugs (antibiotics).
Viruses
Not cells (nucleic acid core with protein coat that cannot reproduce alone). Some have envelope derived from host cell membrane. Are intracellular pathogens. Once inside host, virus nucleic acid takes over. New viral particles can either rupture host cell or bud off from host cell. Cannot be killed by antibiotics but some can be treated with antiviral drugs.
Lymphoid Organs
Immune system organs where lymphocytes are found. Are connected by blood vessels and the lymph vessels.
Bone Marrow
Where all blood cells originate. B lymphocytes mature here.
Thymus
Where T lymphocytes mature.
Afferent Lymph Vessel
Brings in lymphocytes from the periphery (outside).
Efferent Lymph Vessel
Allows lymphocytes to keep circulating.
Encapsulated Secondary Lymphoid Organs
Spleen and lymph nodes via a fibrous wall.
Unencapsulated Secondary Lymphoid Organs
Tonsils and GALT (diffusion).
6 Main Types of Leukocytes
1) Eosinophils
2) Basophils (Mast Cells)
3) Neutrophils
4) Monocytes (Macrophages)
5) Lymphocytes
6) Dendritic Cells
Degranulate
Spew granule contents.
Macrophages
Are large amoeboid cells and function as scavengers by phagocytosing old red blood cells and dead neutrophils. Can phagocytose up to 100 bacteria. Have a role in adaptive immune response (phagocytosed pathogens are digested and fragments are placed on the cell surface (APCs)).
B in B Cells
Bursa of Fabricius (an invagination of the colon found in chickens. Mammals do not have a bursa).
T Lymphocytes/Cells
Produced in the bone marrow but mature/develop in the thymus. Uses contact-dependent signalling (cell-to-cell communication) via the T-cell receptor expressed on the T cell membrane (can only bind to MHC-antigen complexes). T-cell receptor cannot bind to free antigen.
MHC
Major histocompatibility complex. Are proteins expressed on the surface of cells that display self-antigens and non-self antigens to T cells. Also called Human Leukocyte Antigens (HLA).
Immune Response
Occurs when pathogens overcome the defence system of the body.
Basic Steps of an Immune Response
1) Detection and identification of foreign substance.
2) Communication with other immune cells.
3) Recruitment of help and co-ordination of the response.
4) Destruction or suppression of the invader.
Innate Immune Response
A more rapid, less specific response. Can lead to adaptive responses. Response begins within minutes to hours and it does not remember past infections. Some non-specific cell types and proteins. Inflammation is distinctive in innate immune response.
Adaptive Immune Response
A slower, more specific response. The response takes days to weeks.
Examples of Physical Barriers
Skin, mucous linings or the gut and genital tract, and ciliated epithelium of respiratory system.
Example of Chemical Barriers
Stomach acids.
Extravasation
Phagocytes leave the circulation and enter tissue through capillary walls.
Opsonization
The process of tagging a pathogen for destruction.
Phagosome
The material (pathogen) in a vesicle when digested by a phagocyte.
Phagolysosome
When the phagosome fuses with the lysosome which contain digestive enzymes and chemicals that kill the pathogen.
Pus
Dead phagocytes, tissue fluids, and debris collected at the site of injury.
Interferons
Interfere with viral replication.
IFN α
Induces an antiviral state in nearby cells that prevents viral replication.
IFN β
Induces an antiviral state in nearby cells that prevents viral replication.
IFN γ
Activates macrophages and other immune cells.
Chemical Mediators
Are cytokines that are released by macrophages. Play a role in the innate response. Create the inflammatory response which serves as a signal to attract other cells and chemical agents to the site, increases capillary permeability, and causes fever. A physical barrier is produced which prevents the spread of the pathogen. Tissue repair is promoted.
Interleukin-1 (IL-1)
Mediates the inflammatory response. Effects are mainly local but can be systemic.
Interleukin-1 (IL-1) Functions
1) Act on endothelial cells lining the blood vessels (loosens junctions between cells).
2) Act on liver cells to produce blood proteins involved in damage control.
3) Induce fever.
4) Stimulate cytokine production.
Complement Proteins
Activated by sequential proteolysis. Some are opsonins, some are chemotaxins, and some form the Membrane Attack Complex and make holes in pathogen membranes.
Membrane Attack Complex (MAC)
Formed from complement proteins. Make holes in pathogen membranes which allows ions to enter allowing water to follow resulting in the pathogen to swell and lyse. Results in the MAC Attack!
Specificity
To describe how an individual cell recognizes a specific pathogen.
Primary Immune Response
Happens on the first exposure to an antigen. A slower, delayed response with less antibody concentration.
Secondary Immune Response
Happens much faster (24-48 hours to match primary response level). This is due to it being mediated by memory cells resulting in more antibodies being produced.
Antibody Classes
IgM
IgA
IgD
IgG
IgE
IgM
Produced during primary response. Activates complement.
IgA
Found in secretions. Neutralizes pathogens before entry.
IgD
Found on surface of B cells with IgM. Helps activate B cells.
IgG
75% of plasma antibodies. Secondary response. Activates complement and opsonizes.
IgE
Allergic response. Recognized by mast cells.
Fab Region
The arms of an antibody that contain the binding sites.
Fc Region
The stem of an antibody that determines which of the five classes the antibody belongs to.
Epitope
The specific part of an antigen that the immune system recognizes.
Antibody Functions
1) Act as opsonins to tag pathogens for phagocytosis.
2) Cause antigen/pathogen clumping.
3) Neutralize bacterial toxins.
4) Activate complement.
5) Activate B cells.
6) Activate antibody dependent cellular activity (ex. activate NK cells or eosinophils).
7) Activate mast cells to degranulate.
Perforin
Released by cytotoxic T cells which form pores/holes in the target cell.
Granzymes
Released by cytotoxic T cells which enter through pores/holes in the target cell to trigger apoptosis.
Fas Ligand
A death ligand expressed by cytotoxic T cells which kill the target cell via apoptosis.
4 Different Types of Immune Response Pathways
1) Extracellular Bacteria
2) Intracellular Viruses
3) Allergic Responses
4) Foreign Tissue
Immediate Hypersensitivity
An allergic response that occurs in minutes. Is antibody mediated.
Delayed Type Hypersensitivity (DTH)
An allergic response that takes hours to days. Is mediated by T cells and macrophages.
Localized Allergic Response
Rashes or hay fever.
Systemic Allergic Response
Anaphylactic shock. Widespread vasodilation, circulatory collapse, and bronchoconstriction.
Graft VS Host
Rejection of the host by the donor tissue.
Host VS Graft
Rejection of the donor tissue by the recipient’s immune system.
Effector Cells
Cells that attack the pathogen.
