BISC 227 Chapter 16-2: Lymphatic System and Immunity

Pathway of adaptive (specific) defense

1. Pathogen begins to enter the body

2. First line of defense

3. Pathogen enters body

4. Second line of defense/third line of defense

First line of defense

Mechanical barriers (skin and mucous membranes)

Second line of defense

Chemical barriers (enzymes, pH, salt, interferons, defensins, collectins, complement)

Natural killer cells

Inflammation

Phagocytosis

Fever

Third line of defense

Cellular immune response

Humoral immune response

Antigens

Receptors on the surface of lymphocytes enabling cells to recognize non-self antigens

Examples of antigens

Proteins, polysaccharides, glycoproteins, glycolipids

Large and complex

Most effective antigens are _____ and _____ molecules

Haptens

Small molecules that are not antigenic by themselves, but when they combine with a large molecule in the body, they can evoke an immune response

T lymphocytes (T cells)

Specialize in thymus

After release from thymus, make up 70-80% of circulating lymphocytes

Some settle in lymphatic organs, such as lymph nodes, thoracic duct, white pulp of spleen

B lymphocytes (B cells)

After release from bone marrow, make up 20-30% of lymphocytes in blood

Abundant in lymph nodes, spleen, bone marrow, intestinal lining

T cells

Origin of undifferentiated cell: Red bone marrow

Site of differentiation: Thymus

Primary locations: Lymphatic tissues, 70%-80% of the circulating lymphocytes in blood

Primary functions: Provide cellular immune response in which T cells interact directly with the antigens or antigen-bearing agents, to destroy them

B cells

Origin of undifferentiated cell: Red bone marrow

Site of differentiation: Red bone marrow

Primary locations: Lymphatic tissues, 20%-30% of the circulating lymphocytes in blood

Primary functions: Provide humoral immune response in which B cells interact indirectly, producing antibodies that destroy the antigens or antigen-bearing agents

Antigen-processing cell

T cell activation requires presence of processed fragments of antigen attached to the surface of an _____

Major histocompatibility complex (MHC)

T cell activation begins:

Macrophage phagocytizes bacterium via lysosomes

Bacterial antigens move to macrophage's surface and displayed near protein molecules part of the _____

MHC antigens

Help T cells recognize an antigen is foreign

Class I and class II

Class I MHC antigen

Within cell membrane of all body cells except red blood cells

Class II MHC antigen

On surfaces of antigen-presenting cells, thymus cells, and activated T cells

Helper T cells

Become activated when its antigen receptor combine with displayed foreign antigens

Antibodies

Activated T cell stimulates B cell to produce _____

Cellular immune response

T cells attach to foreign, antigen-bearing cells and interact differently, by cell-to-cell contact→_____ or cell-mediated immunity

Colony-stimulating factors

Stimulate bone marrow to produce lymphocytes

Interleukins (IL-1 & IL-2)

Control lymphocyte differentiation and proliferation

Tumor necrosis factor

Stops tumor growth, releases growth factors, causes fever that accompanies bacterial infection, stimulates lymphocyte differentiation

Interferons

Block viral replication, stimulate macrophages to engulf viruses, stimulate B cells to produce antibodies, attack cancer cells

Helper T cells

CD-4 cell; activate other cells by secreting cytokines; stimulate B cells to produce antibodies and stimulate activity of cutotoxic T cells; any harm to them destroys immunity

Cytotoxic T cells

Attack virally infected or cancerous cells; secrete perforin

Memory T cells

Provide future immune protection

Regulatory T cells

Suppress immune responses after defeat of pathogens, which lowers chance of developing an autoimmune disease

B cells

May become activated upon encountering an antigen

Most antigens require T cell "help" to activate _____

Some differentiate into memory cells and others into plasma cells

Plasma cells

Produce and secrete antibodies→humoral immune response

Millions

Each person has _____ of varieties of T and B cells

Clones

Members of each variety originate from a single cell→_____

Antigen receptor

Each member has specific _____ that respond to specific antigen→antibodies combine with antigen-bearing agent and react against it

Polyclonal response

Singly type of B cell carries info to produce single type of antibody→immune response can have several types of antibodies crated against a single microbe or virus→_____

B cell activities

1. Antigen-bearing agents enter tissues

2. B cell encounters an antigen that fits its antigen receptors

3. Either alone or more often in conjunction with helper T cells, the B cell is activated. The B cell proliferates, enlarging its clone

4. Some of the newly formed B cells differentiate further to become plasma cells

5. Plasma cells synthesize and secrete antibodies whose molecular structure is similar to the activated B cell's antigen receptors

T cell activities

1. Antigen-bearing agents enter tissues

2. An antigen-presenting cell, such as a macrophage, phagocytizes the antigen-bearing agent, and the macrophage's lysosomes digest the agent

3. Antigens from the digested antigen-bearing agents are displayed on the membrane of the antigen-presenting cell

4. Helper T cell becomes activated when it encounters a displayed antigen that fits its antigen receptors

5. Activated helper T cell releases cytokines when it encounters a B cell that has previously combined with an identical antigen-bearing agent

6. Cytokines stimulate the B cell to proliferate, enlarging its clone

7. Some of the newly formed B cells give rise to cells that differentiate into antibody-secreting plasma cells

Antibody molecules

Soluble, globular proteins

4 chains of amino acids linked by disulfide bonds→Y-shaped structures

Two light chains and two heavy chains

End of chains are variable regions→react with shape of specific antigen

Idiotypes

Antibodies can bind with certain antigens due to conformation of variable regions→antigen-binding sites→_____

IgG

80% of antibodies; act on bacteria, viruses, toxins

IgA

13% of antibodies; found in exocrine gland secretions

IgM

6% of antibodies; act on antigens in foods and bacteria

IgD

<1% of antibodies; found on B cell surfaces, common in infants

IgE

<1% of antibodies; found in exocrine gland secretions

Antibody direct attack

Types of effect: Agglutination, precipitation, neutralization

Antibody activation of completement

Types of effect: Opsonization, chemotaxis, agglutination, lysis, neutralization

Antibody localized changes

Type of effect: Inflammation

Agglutination

Antigens clump; clumps antigen-bearing cells

Precipitation

Antigens become insoluble

Neutralization

Antigens lose toxic properties; alters the molecular structure of viruses, making them harmless

Opsonization

Alters antigen cell membranes so cells are more susceptible to phagocytosis

Chemotaxis

Attracts macrophages and neutrophils into the region

Lysis

Allows rapid movement of water and ions into the foreign cell causing osmotic rupture of the foreign cell

Inflammation

Helps prevent the spread of antigens

Primary immune response

Detectable levels of antibodies appear 5-10 days following exposure

Production and release of antibodies continues for several weeks

Secondary immune response

Antibodies may be produced within a day or two of exposure

Naturally acquired active immunity

Mechanism: Exposure to living pathogens

Result: Stimulation of an immune response with symptoms of a disease

Artificially acquired active immunity

Mechanism: Exposure to a vaccine containing weakened or dead pathogens or their components

Result: Stimulation of an immune response without symptoms of a disease

Naturally acquired passive immunity

Mechanism: Antibodies passed to fetus from pregnant woman with active immunity or to newborn through colostrum or breast milk from a woman with active immunity

Result: Short-term immunity for newborn without stimulating an immune response

Artificially acquired passive immunity

Mechanism: Injection of antiserum containing specific antibodies or antitoxin

Result: Short-term immunity without stimulating an immune response

Type I hypersensitivity reaction (immediate-reaction)

Response: Overproduction of IgE antibodies

Example: Hay fever

Type II hypersensitivity reaction (antibody-dependent cytotoxic reaction)

Response: Phagocytosis and complement-mediated lysis of antigen

Example: Mismatched blood transfusion

Type III hypersensitivity reaction (immune complex reaction)

Response: Phagocytosis and lysis cannot clear antigen-antibody complexes

Example: Autoimmunity

Type IV hypersensitivity reaction (delayed-reaction)

Response: T cells and macrophages release chemical factors into the skin

Example: Dermatitis

Tissues and organs that can be transplanted

Bone, cornea, kidney, liver, pancreas, heart, bone marrow, skin, lungs

Tissue rejection reaction

Recipient's cells recognize donor's tissues as foreign and try to destroy transplanted tissue

Graft-versus-host disease (GVHD)

Transplanted tissue may produce substances that harm recipient's tissues

Rapid and severe

The greater the antigenic difference between MHC antigens of recipient and donor tissues, more _____ and _____ the rejection reaction

Match

Attempt to _____ donor tissues that are antigenically like those of the person needing transplant

Isograft

Donor: Identical twin

Example: Bone marrow transplant from a healthy twin to a twin who has leukemia

Autograft

Donor: Self

Example: Skin graft from one part of the body to replace burned skin

Allograft

Donor: Same species

Example: Kidney transplant from a relative or closely matched donor

Xenograft

Donor: Different species

Example: Heart halves from a pig

Autoimmunity

An attack by the immune system against its own tissues

Autoantibodies

The immune system fails to distinguish "self" from "non-self" and the body produces antibodies called _____

Cytotoxic

_____ T cells also attack the body's tissues and organs

Autoimmune disorders

Various _____ affect different types of cells

There are several theories concerning the cause(s) of _____, but no single cause has been established

Glomerulonephritis

Symptoms: Lower back pain

Antibodies against: Kidney cell antigens that resemble streptococcal bacteria antigens

Graves' disease

Symptoms: Restlessness, weight loss, irritability, increased heart rate and blood pressure

Antibodies against: Thyroid gland antigens near thyroid-stimulating hormone receptor, causing overactivity

Type 1 diabetes mellitus

Symptoms: Thirst, hunger, weakness, emaciation

Antibodies against: Pancreatic beta cells

Hemolytic anemia

Symptoms: Fatigue and weakness

Antibodies against: Red blood cells

Multiple sclerosis

Symptoms: Weakness, incoordination, speech disturbances, visual complaints

Antibodies against: Myelin in peripheral nerves and in the white matter of the central nervous system

Myasthenia gravis

Symptoms: Muscle weakness

Antibodies against: Receptors for neurotransmitters on skeletal muscle

Pernicious anemia

Symptoms: Fatigue and weakness

Antibodies against: Binding site for vitamin B on cells lining stomach

Rheumatic fever

Symptoms: Weakness, shortness of breath

Antibodies against: Heart valve cell antigens that resemble streptococcal bacteria antigens

Rheumatoid arthritis

Symptoms: Joint pain and deformity

Antibodies against: Cells lining joints

Systemic lupus erythematosus

Symptoms: Red rash on face, prolonged fever, weakness, kidney damage, joint pain

Antibodies against: Connective tissue

Ulcerative colitis

Symptoms: Lower abdominal pain

Antibodies against: Colon cells

HIV (Human Immunodeficiency Virus)

A virus that breaks down immune system function

AIDS (Acquired Immune Deficiency Syndrome)

HIV may stay silent for years, and then progress to _____; then opportunistic infections begin

Macrophages and helper T cells

HIV attacks _____ and then _____

Decline

Helper T cell numbers _____→B cells cannot produce antibodies

Cytotoxic T cells

Later, HIV variants affect _____ too

Dies

Person with HIV/AIDS _____ from loss of immune response against pathogens, cancers

HIV/AIDS modes of transmission

Sexual contact, contaminated needles, birth or milk from infected mother, receiving infected blood or tissues from donor