Unit 6: Immune System

What is the ability to fight off other smaller organisms in big multicellular organism's internal environment called?

Immunity (immunis = exempt)

What are the three key features of the immune system?

Lymphoid tissues, immune cells, and chemicals that coordinate and execute function

What are the three main functions of the immune system?

Protecting the body, removing dead/damaged tissue and cells, and recognizing/removing abnormal cells

What are three examples of abnormal immune system performance?

Incorrect responses (autoimmunity), overactive responses (allergies), and lack of responses (immunodeficiency)

What are pathogens? What are two major types?

Disease causing agents; viruses & bacteria are the two major types

True or False: The immune response generated by one pathogen will be exactly the same as that of another pathogen.

False - Different pathogens require different immune responses

where can bacteria reside in the body vs viruses

bacteria → intracellular and extracellular (in ecf). can live and reproduce without host

viruses → intracellular. need host

What class of drug can kill most bacterial infections?

Antibiotics

what are viruses

nucleic acid (DNA or RNA) with protein coat → not cells. can have envelopes derived from host cell membrane

what do viruses do once they take over host cells

either rupture host or bud off from host cell

What class of drug can kill some viral infections

Antivirals

what are immune system organs called

lymphoid organs → they contain lymphocytes (B/T/NKcells)

how are lymphoid organs connected to one another

via blood vessels and lympth vessels

what is lymph

clear fluid within lymph vessels → collection of ECF that left capillaries and filtered through tissue

what does lymph act as

conduit for immunologically active cells to travel through

Where are lymph nodes located? Why are these locations strategic for immune function?

Knee, groin, elbow, shoulder, neck → major areas of lymph drainage

What is the region of the body outside of lymphoid organs referred to as

periphery

What are the two types of lymphoid organs?

primary → where lymphocytes develop

secondary → where lymphocytes interact and initiate response

examples primary lymphoid organs

• bone marrow → all blood cells originate here, B lymphocytes mature here

• thymus → T cells mature here

4 secondary lymphoid organs

Spleen, lymph nodes, tonsils, and Gut Associated Lymphoid Tissue (GALT)

what are secondary lymphoid tissues doing as they filter through blood and lymph

look for pathogens and pathogen-containing lymphocytes

afferent vs efferent lymph vessels in secondary lymphoid tissue

afferent → bring in lymphocytes from the periphery

efferent → allow lymphocytes to leave and continue circulating

What occurs in the pulp inside lymph nodes?

mixing of lymphocytes and other leukocytes for pathogen detection

What do arteries and veins of the lymphatic system do?

Supply nutrients, O2, and non-lymphatic leukocytes to lymphoid tissue

encapsulation of seconardary lymphoid tissue

spleen and lymph nodes → encapsulated by fibrous wall (feel hard upon swelling)

tonsils and GALT → unencapsulated/diffuse tissues

What type of blood cell are main players in the immune system?

Leukocytes (WBC) → bigger than RBC but less numerous in circulation (not necessarily in total)

True or False: Leukocytes (WBC) can leave the blood stream and function extracellularly

True - This allows them to function in the tissues during immune response.

What are the six main types of leukocytes?

never let monkeys eat bananas daily

• Eosinophils, Basophils (Mast Cells), Neutrophils, Monocytes (Macrophages), Lymphocytes, Dendritic Cells

True or False: All Leukocytes have the same lifespan.

False - Leukocyte lifespans can range from only a few hours to several months

what are the four categories of leukocytes in the immune system

Granulocytes, Phagocytes, Cytotoxic Cells, and Antigen Presenting Cells (APCs)

what are the four categories of leukocytes in the immune system: granulocytes

contain prominent cytoplasmic granules → neutrophils, eosinophils, and basophils

what are the four categories of leukocytes in the immune system: phagocytes

engulf and ingest pathogens → neutrophils, macrophages, and dendritic cells

what are the four categories of leukocytes in the immune system: cytotoxic cells

kill other cells (even self cells) via apoptosis → eosinophils and some lymphocytes

what are the four categories of leukocytes in the immune system: antigen presenting

display fragments of pathogens on cell surface → some lymphocytes, dendritic cells, and macrophages

What are antigens?

Ag: antibody generator → recognized by an antibody and induces immune response

What is an anitbody?

Ab, proteins that bind to antigens and target pathogens for destruction

True or False: Granulocytes do not degranulate in allergic responses.

False - Eosinophils and Basophils are granulocytes vital to allergic reactions.

What are eosinophils and their characteristics?

cytotoxic granulocytes with pink staining granules → role in parasitic infections and allergic responses.

Where are eosinophils found? How long do they live?

In peripheral circulation in the digestive tract, lungs, genital tract, and skin; they live for 6-12 hours

What happens when an eosinophil encounters a parasite or allergen?

bind to antibody-coated parasite (or encounter allergen) and degranulate → spew toxic enzymes and oxidative chemicals that damage/kill allergens/parasites

What are basophils and their characteristics?

granulocytes with large dark blue staining granules → predominantly involved in allergic responses

Where are basophils/mast cells located

basophils → small numbers in blood

mast cells → in tissue (digestive tract, lungs, and skin)

What happens when a basophil encounters an allergen?

They degranulate, releasing histamine, heparin, and cytokines from their granules

True or False: The most abundant leukocyte in the body is neutrophils.

True

What are neutrophils and their characteristics?

phagocytic granulocytes → can ingest 5-20 bacteria.

Where are neutrophils located? How long do they live?

can leave the circulatory system to attack pathogens in tissues. live 1-2 days.

What happens when a neutrophil degranulate

release cytokines that cause fever/other inflammatory responses

What are monocytes and their characteristics?

precursor cells of tissue macrophages

Where are monocytes located? How long do monocytes live?

circulate in the blood → live there for ~8 hours, then move to tissues to become macrophages

What are macrophages and their characteristics?

large, ameboid-like, antigen-presenting phagocytes → scavenge old red blood cells, dead neutrophils, and bacteria; involved in adaptive immunity

What happens when a macrophage phagocytoses a pathogen?

engulf and digest pathogen, then display fragments of the pathogen on its cell surface

What are lymphocytes and their characteristics?

Key players in adaptive immunity, mostly in secondary lymphoid tissue not circulation

True or False: You can distinguish what kind of lymphocyte you are examining simply based on appearance

False - Lymphocytes look alike under a microscope but have fundamental differences in functions

How many lymphocytes are there in the body at a given time?

10^12 → lots!

What are dendritic cells and their characteristics?

phagocytic APCs with long thin processes.→ key role in adaptive immunity

Where are dendritic cells located?

skin and other organs

What happens when a dendritic cell encounters a pathogen?

recognize, engulf and digest pathogens, then display fragments on cell surface

What does it mean when a dendritic cell is "Activated"?

means it’s presenting cell fragments → migrate to secondary lymphoid organs to show lymphocytes

types of lymphocytes

B lymphocytes (B cells), T lymphocytes (T cells) and NK cells

types of lymphocytes: B cell role

produce antibodies → can act as surface receptors or be secreted into the plasma. also phagocytize as a side role

Where are B Lymphocytes produced? Where do they develop?

produced in the bone marrow, mature in the spleen and lymph nodes

What does the "B" in B Lymphocytes mean?

short for "Bursa-equivalent" → reference to the Bursa of Fabricius, an invagination of the colon found in chickens (not humans)

What is the shape of an antibody?

"Y" Shaped

types of lymphocytes: T cell role

use contact-dependent signaling via their membrane T-cell receptors → bind to MHC-antigen complexes NOT free Ag’s

Where are T Lymphocytes produced? Where do they mature?

produced in bone marrow, mature in the thymus (why theyre called T cells)

What is a Major Histocompatibility Complex (MHC)?

proteins expressed on the surface of cells that display "self-antigens" and "non-self antigens" to T cells → vary between individuals, only same in identical twins

MHC class I vs MHC class II

• Class I → on all nucleated cells

• Class II → only on APCs

True or False: erythrocytes have MHC class I.

False - have no nucleus, so do not display MHC I. do display MHC II

the three subtypes of T cells

Cytotoxic (Tc), Helper (Th), Regulatory (Treg)

the three subtypes of T cells: cytotoxic (T_c or killer T cells)

recognize antigens presented on class I MHC and kill non-self antigens. have CD8 protein

the three subtypes of T cells: helper (T_H)

recognize antigens presented on class II MHC and promote differentiation of B cells & Tc cells. also activate macrophages.

“hate the one” and “help the 2”

hate for CD8 → hate (cytotoxic T cells) recognize MHC class I

help for CD4 → helper and regulatory T cells recognize MHC class II

rule of 8’s

• cells containing CD4 (T_H + T_regs) interact with class II MHC; 4×2=8

• cells containing CD8 (T_c) interact with class I MHC; 8×1=8

the three subtypes of T cells: regulatory (T_regs)

recognize antigens presented on class II MHC and prevent excessive immune response by suppressing other immune cells

What are the four basic steps of an immune response regardless of the foreign substance?

• detection/identification

• communication with other immune cells

• recruitment of help/response coordination

• destruction/suppression of invader

What two substances does the immune system use for chemical signalling?

Antibodies (bind to antigens as signals) and cytokines (affect growth or activity)

two branches of immunity

Innate and Adaptive immunity → overlap and interact

other names for adaptive immunity

specific or acquired immunity

two branches of immunity: innate

rapid, non-specific response → can lead to adaptive response

• Inflammation is a distinct innate immune response

two branches of immunity: adaptive

slow, specific response that develops memory

What are the two divisions of adaptive immunity?

cell-mediated immunity and antibody-mediated immunity (AKA humoral immunity)

True or False: Adaptive immunity is only found in invertebrates.

True - This is unlike innate immunity which all organisms have.

What lymphocyte is related to cell-mediated immunity?

T-Lymphocytes

What lymphocyte is related to antibody-mediated (aka humoral) immunity?

B-Lymphocytes

What are our first and second line of innate immune defense?

• first line of defense → physical and chemical barriers

• second line → leukocytes & blood proteins. same reaction to every infection

innate immunity first line of defense example components

• skin

• mucous lining of gut and genital tract

• ciliated epithelium of respiratory system

• stomach acids

role of innate immunity in relation to adaptive immunity

contains pathogen until adaptive response kicks in

the majority of innate immune system cells are ___

phagocytes → ingest invaders

what are the cells of innate immunity

mast cells, NK cells, monocytes/macrophages, neutrophils

chemotaxins

chemicals that attract other immune cells

• cytokines/other immune blood proteins

• tissue injury products (fibrin)

• bacterial products

extravasation

when phagocytes leave circulation and enter tissues through capillary walls → capillary endothelial cells loosen junctions to allow this

How do phagocytes identify invaders?

via chemical cues → interact with receptors on the phagocyte membrane

phagosome

found in phagocytes → vesicle containing engulfed particle

How do phagocytes move to engulf invaders

pseudopodia (false feet) are aided by actin filaments to push the cell around the invader

What happens if a pathogen doesn't have surface features that can be recognized directly by phagocytes?

blood proteins bind to and coat the pathogen, "tagging" it for phagocytes receptors to recognize → known as opsonization

What is an opsonin?

protein that can "tag" an invader that doesn’t have recognizable surface features

• eg antibody

phagolysosomes

Phagosomes fused with a lysosome (contains digestive enzymes)

What is pus?

Dead phagocytes, tissue fluids, and debris collecting at the site of an injury

What happens after a phagocyte digests an antigen if its also an antigen-presenting cell?

presents digested bacteria on the surface on MHC class II

What are innate lymphocytes called?

NK cells → act within minutes with non-specific responses for pathogen-infected and cancerous cells. trigger apoptosis