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Immune System Gissel Hernandez per. 5 - Coggle Diagram
Immune System
Gissel Hernandez
per. 5
Artificially vs. Naturally acquired immunity
Active humoral immunity occurs when B cells encounter antigens and produce
specific antibodies against them
Two types of active humoral immunity
Naturally acquired: formed in response to
actual bacterial or viral infection
Artificially acquired: formed in response to
vaccine of dead or attenuated pathogens
Passive humoral immunity occurs when ready-made antibodies are introduced into
body
B cells are not challenged by antigens; Immunological memory does not occur
Protection ends when antibodies degrade
Two types of passive humoral immunity
Naturally acquired: antibodies delivered to fetus via placenta or to infant
through milk
Artificially acquired: injection of serum, such as gamma globulin
Protection immediate but ends when antibodies naturally degrade in body
Line of Defenses
• Surface barriers are skin and mucous membranes, along with their secretions
Physical barrier to most microorganisms
– Keratin is resistant to weak acids and bases, bacterial enzymes, and toxins
– Mucosae provide similar mechanical barriers
• Skin and mucous membranes produce protective chemicals that inhibit or destroy microorganisms
– Acid: acidity of skin and some mucous secretions inhibits growth; called acid mantle
– Enzymes: lysozyme of saliva, respiratory mucus, and lacrimal fluid kills many microorganisms; enzymes in stomach kill many microorganisms
– Mucin: sticky mucus that lines digestive and respiratory tract traps microorganisms
• Respiratory system also has modifications to stop pathogens
– Mucus-coated hairs in nose trap inhaled particles
– Cilia of upper respiratory tract sweep dust- and bacteria-laden mucus toward mouth
• Surface barriers breached by nicks or cuts trigger the internal second line of defense that protects deeper tissues
• Innate system necessary if microorganisms invade deeper tissues; includes:
Phagocytes
Natural Killer (NK) Cells
Inflammatory response (macrophages, mast cells, WBCs, and inflammatory chemicals)
Antimicrobial proteins (interferons, and complement proteins)
Fever
-Many second-line cells have pattern recognition receptors that recognize and bind tightly to structures on microbes, disarming them before they do harm
Phagocytes: white blood cells that ingest and digest (eat) foreign invaders
-Neutrophils: most abundant phagocytes, but die fighting; become phagocytic on exposure to infectious material exposure to infectious material
Macrophages: develop from monocytes and are chief phagocytic cells; most robust phagocytic cell
Natural Killer (NK) Cells
Nonphagocytic, large granular lymphocytes that police blood and lymph
– Can kill cancer and virus-infected cells before adaptive immune system is activated
-Attack cells that lack “self” cell-surface receptors
Kill by inducing apoptosis in cancer cells and virus-infected cells
Secrete potent chemicals that enhance inflammatory response
Antigens and Antibodies
Antigens: substances that can mobilize adaptive defenses and provoke an immune
response
Targets of all adaptive immune responses
Characteristics of antigens:
Can be a complete antigen or hapten (incomplete)
Contain antigentic determinants
Can be a self-antigen
Self-antigens: all cells are covered with variety of proteins located on surface that are not antigenic to self, but may be antigenic to others in transfusions or grafts
One set of important self-proteins are group of glycoproteins called MHC proteins
Coded by genes of major histocompatibility complex (MHC) and unique to each individual
Contain groove that can hold piece of self-antigen or foreign antigen
T lymphocytes can recognize only antigens that are presented on MHC
proteins
Antigen-presenting cells (APCs)
Do not respond to specific antigens
Play essential auxiliary roles in immunity
Engulf antigens and present fragments of antigens to T cells for recognition
Major types:
Dendritic cells
Found in connective tissues and epidermis
Act as mobile sentinels of boundary tissues
Phagocytize pathogens that enter tissues, then enter lymphatics to present antigens to T cells in lymph node
Most effective antigen presenter known
Key link between innate and adaptive immunity
Macrophages
Widely distributed in connective tissues and lymphoid organs
Present antigens to T cells, which not only activates T cell, but also further activates macrophage
Activated macrophage becomes phagocytic killer
Also trigger powerful inflammatory responses and recruit additional defenses
B lymphocytes
Do not activate naive T cells
Present antigens to helper T cell to assist their own activation
Antibodies
Antibodies—also called Immunoglobulins (Igs)—are proteins secreted by plasma cells
capable of binding specifically with antigen detected by B cells, grouped into one of 5 Ig classes
Basic antibody structure:
Overall T- or Y-shaped antibody monomer consists of four looping polypeptide
chains linked by disulfide bonds
Four chains consist of:
Two identical heavy (H) chains with hinge region at “middles”
Two identical light (L) chains
Variable (V) regions at one end of each arm combine to form two identical
antigen-binding sites
Stems make up constant (C) regions
Five major classes: IgM, IgA, IgD, IgG, and IgE
Antibody targets and functions:
Antibodies do not destroy antigens; they inactivate and tag them
Form antigen-antibody (immune) complexes
Defensive mechanisms used by antibodies:
Neutralization
Simplest, but one of most important defensive mechanism
Antibodies block specific sites on viruses or bacterial exotoxins
Prevent antigens from binding to receptors on tissue cells
Antigen-antibody complexes undergo phagocytosis
Aggultination
Allows for antigen-antibody complexes to become cross-linked into large
lattice-like clumps
Process referred to as agglutination
Example: clumping of mismatched blood cells
Precipitation
Soluble molecules (instead of cells) are cross-linked into complexes
Complexes precipitate out of solution
Precipated complexes are easier for phagocytes to engulf
Complement fixation and activation
Main antibody defense against cellular antigens (bacteria, mismatched RBCs)
When several antibodies are bound close together on same antigen,
complement-binding sites on their stem regions are aligned
Antigen-antibody complexes do not destroy antigens; they prepare them for
destruction by innate defenses
Antibodies go after extracellular pathogens; they do not invade solid tissue unless
lesion is present
Recent exception found: antibodies can act intracellularly if attached to virus
before it enters cell, activate mechanisms that support virus
Location of Lymphatic Organs and Functions
Lymphoid organs are grouped into two functional categories
Primary lymphoid organs: areas where T and B cells mature—red bone marrow
and thymus
T and B cells originate in bone marrow, but only B cells matures there; T cells
mature in thymus
Secondary lymphoid organs: areas where mature lymphocytes first encounter
their antigen and become activated
Nodes, spleen, MALT (mucosa-associated lymphoid tissue) and diffuse
lymphoid tissues
Spleen:
Spleen is blood-rich organ about size of fist, located in left side of abdominal cavity, just below stomach
Functions
Site of lymphocyte proliferation and immune surveillance and response
Cleanses blood of aged blood cells and platelets; macrophages remove debris
MALT:
Mucosa-associated lymphoid tissue (MALT)
Lymphoid tissues in mucous membranes throughout body
Found in mucosa of respiratory tract, genitourinary organs, and digestive tract; largest collections of MALT found in tonsils, peyer's patch, appendix
Tonsils:
Simplest lymphoid organ, form ring of lymphatic tissue around pharynx; appear as swellings of mucosa
Named according to location
Palatine tonsils: at posterior end of oral cavity (largest tonsils most often infected)
Lingual tonsil: lumpy collection of follicles at base of tongue
Pharyngeal tonsil: also called adenoids; located in posterior wall of nasopharynx
Tubal tonsils: surround openings of auditory tubes into pharynx
Tonsils function is to gather and remove pathogens in food or air
Peyer's Patch (aggregated lymphoid nodules)
clusters of lymphoid follicles in wall of distal portion of small intestine
Location aids in functions
Destroy bacteria, preventing them from breaching intestinal wall
Generate “memory” lymphocytes
Appendix:
offshoot of first part of large intestine, contains a large number of lymphoid follicles
Location aids in functions (like Peyer’s patches)
Thymus:
bilobed lymphoid organ found in inferior neck, extends into mediastinum and partially overlies heart
Functions as lymphoid organ where T cells mature
Most active and largest in size during childhood
Stops growing during adolescence, then gradually atrophies
Still produces immunocompetent cells, though more slowly
Thymus is broken into lobules that contain outer cortex and inner medulla
Cortex contains rapidly dividing lymphocytes (the bulk of thymic cells) and
scattered macrophages
Medulla contains fewer lymphocytes and thymic corpuscles
Thymic corpuscles are where regulatory T cells develop
Regulatory T cells: type of T cell that helps to prevent autoimmunity
Innate and Adaptive Immune Defenses
Adaptive immune system is a specific defensive system that eliminates almost any
pathogen or abnormal cell in body
Characteristics of adaptive immunity:
It is specific: recognizes and targets specific antigens
It is systemic: not restricted to initial site
It has memory: mounts an even stronger attack to “known” antigens (second and
subsequent exposures)
Two main branches of adaptive system:
Humoral immunity:
Antibodies, produced by lymphocytes, circulate freely in body fluids
Bind temporarily to target cell
Mark for destruction
Cellular Immunity:
Lymphocytes act against target cell
Directly—by killing infected cells
Indirectly—by releasing chemicals that enhance inflammatory response; or
activating other lymphocytes or macrophages
Innate system uses the first and/or second lines of defense to stop attacks by
pathogens (disease-causing microorganisms)
Cells in Immune System
Macrophages: develop from monocytes and are chief phagocytic cells, robust
Neutrophils: most abundant phagocytes, but die fighting become phagocytic on exposure to infectious material
Phagocytes: WBCs that ingest and digest foreign invaders
Major Functions of Lymphatic and Immune System
Immune system provides resistance to disease
• Made up of two intrinsic systems
– Innate (nonspecific) defense system
▪ Constitutes first and second lines of defense
– First line of defense: external body membranes (skin and mucosae)
– Second line of defense: antimicrobial proteins, phagocytes, and other
cells (inhibit spread of invaders; inflammation most important mechanism)
– Adaptive (specific) defense system
▪ Third line of defense attacks particular foreign substances (takes longer to react than innate)
• Immune system is a functional system rather than organ system
• Innate and adaptive defenses are intertwined
– Both release and recognize many of the same defensive molecules
– Innate defenses do have specific pathways for certain substances
– Innate responses release proteins that alert cells of adaptive system to foreign molecules
Humoral and Cellular Response
• T cells provide defense against intracellular antigens
– Example: cells infected with viruses or bacteria, cancerous or abnormal cells, foreign (transplanted) cells
• Some T cells directly kill cells; others release chemicals that regulate immune response
• T cells are more complex than B cells both in classification and function
• Two populations of T cells
– CD4 cells usually become helper T cells (TH) that can activate B cells, other T cells, and macrophages; direct adaptive immune response
• Some become regulatory T cells, which moderate immune response
– Can also become memory T cells
– CD8 cells become cytotoxic T cells (TC) that are capable of destroying cells harboring foreign antigens
▪ Also become memory T cells
• Helper, cytotoxic, and regulatory T cells are activated T cells
• Naive T cells are simply termed CD4 or CD8 cells
Humoral immunity
– Antibodies, produced by lymphocytes, circulate freely in body fluids
– Bind temporarily to target cell
▪ Mark for destruction
Cellular Immunity
– Lymphocytes act against target cell
▪ Directly—by killing infected cells
▪ Indirectly—by releasing chemicals that enhance inflammatory response; or activating other lymphocytes or macrophages
Passive vs. Active
Active and Passive Humoral Immunity
• Active humoral immunity occurs when B cells encounter antigens and produce
specific antibodies against them
– Two types of active humoral immunity
Naturally acquired: formed in response to actual bacterial or viral infection
Artificially acquired: formed in response to vaccine of dead or attenuated pathogens
• Passive humoral immunity occurs when ready-made antibodies are introduced into body
– B cells are not challenged by antigens; Immunological memory does not occur
– Protection ends when antibodies degrade
– Two types of passive humoral immunity
Naturally acquired: antibodies delivered to fetus via placenta or to infant trhough milk
Artificially acquired: injection of serum, such as gamma globulin
– Protection immediate but ends when antibodies naturally degrade in body
Disorders
Pinworm:
Small round worm called Enterovirus rermeulars that lives in small intestine
Causes/ Risk Factors
swallowing pinworm eggs, breathing/ inhaling eggs, found everywhere easier to get infected
Symptoms
itchy in anal region, weight loss, loss of apettite
Meningitis:
Inflammation of protective membranes covering brain and spinal cord
Hepatitis B:
Inflammation of liver
Toxoplasmosis (parasite):
Caused by microparasite called protozoan
Hands, foot, and mouth disease:
An illness that's from a variety of viruses affecting hands, foot, and mouth
Polio Disease:
Virus that can cause paralysis
Measles:
Highly contagious airborne viral disease evolved from rinderpest
Cholera:
Accute diarrheal illness caused by infection of intestine
Pertussis (whooping cough):
Contagious respiratory illness caused by bordetella pertussis
Rubella:
Contaigious disease caused by virus
Varicella (chicken pox)
Contagious disease caused by varicella zoster virus
Hib:
Bacterial illness that can cause potential deadly brain infection
Tetanus:
bacterial infection causing painful muscles contraction
Malaria:
life threatening disease caused by parasite infection
Small pox:
Infectious disease caused by variola virus
Tuberculosis
Caused by germs spread through person to person through air