HSCI 100 Immune system

Infectious agents

Microbes: microscopic organisms such as bacteria and viruses that can cause disease

Pathogens: microscopic organisms + fungus, parasites and prions(misfolded proteins)

Infection: when pathogen colonizes a tissue that can support its

growth

A pathogen is contagious if it can spread

the 3 lines of immune defense

1. Non-specific physical and chemical barriers

2. Non-specific inflammatory response and

proteins

3. A specific and adaptive or learned response

from the T and B cells

Innate

first 2 lines of defense

No memory (does not “learn”)

Non-specific

Fast

Adaptive/Acquired

3rd line of defense

Memory (learns)

Primed

Specific

Slow (days to weeks)

1st line of defense

physical and chemical barriers:

tears, skin, saliva, large intestine, respiratory tract, stomach and bladder.

2nd line of defense

internal defenses

Inflammation

Cellular phagocytosis

Natural killer cells

Complement system

Organs of the immune system

Lymphatic organs

Primary– Red bone marrow, Thymus gland

Secondary– Lymph nodes, spleen, Peyer’s patches, tonsils, and appendix

Red bone marrow

– Blood cell production

– Some white blood cells mature there

– More bones in children have red marrow and it

decreases as we age

Thymus gland

located in chest cavity behind sternum

Largest in children, shrinks as we age

Immature T cells move from the bone marrow to the thymus where they mature and likely stay

→Only T cells that recognize ‘non-self’ antigens will become active. Self-recognizing T cells are eliminated

Lymph nodes

oval shaped structures found along the lymphatic vessels filled with B cells, T cells and macrophages

Spleen

In the upper left region of the abdominal cavity

– Filled with white pulp that contains B and T lymphocytes and red pulp which is invovled in recycling dead red blood cells

Peyer's patches

clusters of lymphoid tissue in the small intestine monitoring intestinal bacteria

Appendix

small finger like projection near start of large intestine. Vestigial organ that has lymphoid tissue role early in life, but becomes non-essential

The second line of defense:

phagocytic white blood cells

Neutrophils and macrophages both leave circulation and move into

tissue

Extravasation/diapedesis (leukocytes pass through the walls of blood vessels into surrounding tissues)

The second line of defense: inflammatory response

4 symptoms of inflammation: redness, heat, swelling, and pain

-mast cells and basophils releases compounds like histamine that trigger inflammation and allergic reactions.

-pus is mostly dead neutrophils

if neutrophils can’t fully control the damage, cytokines

(secreted by lymphatic cells)

promote more white blood cells in that area

third line of defense:

B and T cells adaptive and specifi

attacks when 1st and 2nd defense fails

Relies on antigen recognition

• Many B and T cells are generated in response to existing antigens

• Attacks cancer cells

B cells

matures in the bone marrow, and recognize antigens directly on pathogens (antibody-mediated immunity) and produce antibodies to fight infections

T cells

produced in the bone marrow, matures in the thymus and respond directly to

antigens presented by other cells (cell-mediated immunity). T cells can either kill infected cells directly or help regulate the immune response.

Antibody-mediated immunity by B cells

the production of antibodies by B cells in response to foreign substances, such as bacteria and viruse

results in clonal expansion

plasma cells are the most activate b cells

other b cells become memory cells which result in long term immunity

plasma cells undergo apoptosis after infection, but memory cells survive

antibody structure

Y-shaped protein assemblies:

2 heavy chains

– 2 light chains

– Joined by disulfide bonds

The end of the two arms are the variable regions that bind to

specific antigens

-by binding to the antigen, it marks it as a foreign entity to be destroyed.

Cell-mediated immunity by T cells

-Each t cell has a receptor called TCR that will recognize an antigen with the help of an antigen-presenting cell(APC)

-The antigen presenting cell(APC) engulfs the antigen and breaks it into small peptides and presents it on its surface. They do this using (MHC) proteins, allowing T cells to recognize and respond to pathogens

-Clonal expansion of T cell prompt helper T cells to recruit B cells and activate cytotoxic T cells (which kill infected cells) and memory T cells(which “remembers” antigens)

-after infection helper T cells and killer T cells undergo apoptosis, but memory T cells survive.

Acquired immunity

-ability to combat infectious diseases and cancer

-long lasting

-depends on clonal selection and production of memory B and T cells

-Immunization can happen naturally or artifically (through vaccines)

Clonal selection: the four predictions

process in the immune system where specific B or T lymphocytes are activated by antigens

1) Each lymphocyte has a unique receptor

2) The receptor must bind to an antigen for activation

3) Activated lymphocytes create clones

4) Clones produce identical receptors and antibodies specific to the antigen.

Allergies

Hypersensitivities to harmless substances

-Immediate allergic responses are caused by the IgE antibodies that attach to mast cells and basophils. This causes histamine to be released, causing allergy reactions.

-Delayed allergic responses are initiated by memory T cells

autoimmune disease

when killer T cells or antibodies attack the body’s own cells

Examples: Lupus, diabetes

Immunodeficiency disease

when the immune system is compromised and thus unable to defend the body against disease

Examples: 

AIDS: 

HIV infects macrophages and helper T cells

SCID:

Severe combined immunodeficiency