Module 1

Approximately how many cells does the human body contain? How does this compare to the amount of microorganisms?

The human body contains approximately 10^13 human cells and ten times as many microorganisms (10^14).

Do humans have more human cells or bacterial cells?

Humans carry more bacterial cells than human cells

What is the good:bad ratio of microorganisms in our microbiome?

Our microbiome contains a larger portion of microorganisms that are harmless or beneficial to our health and functioning and a smaller proportion of pathogenic types that can cause a disease state

Can disease-causing microorganisms get past the first barrier of the immune system?

In most cases, disease-causing microorganisms never get past the first barrier of the immune system. However, for those that do, the immune system is a highly sophisticated system that can recognize, neutralize and eliminate pathogens without harming other cells

The Immune System

Organization of cells, tissues and organs within the body that each have their own specialized role in defending against infection

What are the two major components of the immune system?

• Innate immune system

• Adaptive immune system

What kind of environment does the human body provide for microbes?

The human body provides an ideal environment for many microbes

What is the role of the immune system with regards to microbes?

The immune system works to keep microbes from entering the body. If this fails, it must identify these microbes and destroy them.

Immune Response

The reaction of immune cells to the presence and actions of microbes or danger signals in the body

When the immune system recognizes the presence and actions of microbes in the body what response occurs?

When the immune system recognizes the presence and actions of microbes in the body an immune response occurs.

What are the two main functions of the immune system?

• Discrimination (recognize self from non-self)

• Elimination (destroy non-self, such as pathogens and altered self cells, such as cancer)

What are the two main disfunctions of the immune system?

• Autoimmunity or Hypersensitivity (misdirected or overly active immune system)

• Immunodeficiency (underactive immune system, such as acquired immunodeficiency syndrome/AIDS)

Antigen

Foreign protein that induces an immune response

What do antigens typically include the production of?

Antigens typically include the production of antibodies

What words is antigen a contraction of?

Antibody generator

Antibody

Protein that is produced in response to and countering a specific antigen

What is the relationship between antigens and antibodies?

Antibodies bind to antigens in the body and provide a signal for their elimination

What is the most important property of a property functioning immune system?

Immune system must be strong enough to defend against foreign threats but also controlled and regulated so it doesn’t damage the body’s own tissues

How can the body produce a coordinated response to the introduction of a foreign antigen?

Given that the immune system is made of tissues, organs and specialized cells are shared with other systems the body can produce a coordinated response to the introduction of a foreign antigen

Why does the lymphatic system have an important role in immunity?

The lymphatic system has an important role in immunity because the lymphatic system and immune system share many organs called lymphoid organs

What does the term, “lymphoid” pertain to?

Lymphoid is an adjective pertaining to components of the lymphatic system

What cells of the adaptive immune system are commonly found in lymph? What are they called?

B-cells and T-cells are cells of the adaptive immune system most common commonly found in lymph. Thus, this prompts the term lymphocytes

What three body systems create an efficient filtering system for the body?

The circulatory and immune system create an efficient filtering system for the body

Lymph

Colourless fluid containing white blood cells that bathes the tissues and drains through the lymphatic system into the bloodstream

Interstitial Space

Fluid filled areas that surround the cells of a given tissue

Lymphatic System

Network of vessels that drains fluid called lymph that filtrated from the blood in the capillaries and entered surrounding tissues called interstitial space

How does the circulatory system interact with lymph?

The circulatory system is where lymph comes from and goes after being filtered as the lymphatic vessels distributed throughout the body pick up lymph and carry it towards the heart, where it will re-enter the circulatory system

How do the circulatory and lymphatic systems work together during an immune response?

Cells of the immune system travel between the circulatory and lymphatic system

How do immune cells interact with antigens? How does this differ from mature cells?

Some human cells reside in the tissues and can directly interact with an antigen following the breach of the first immune barrier. Other mature, immune cells travel within the blood to the site of infection where they enter the tissues and bind the antigen, where they then enter the lymphatic system and travel to the lymph nodes, where the antigens are eliminated

What is the primary role of major lymphoid organs and tissues in the immune system?

These organs primarily act as sites for immune cell generation, training, and/or sites of action

What is the structure of bone marrow?

Bone marrow is a flexible tissue filled with haematopoietic cells

Haematopoietic cells

Cells lodged within the bone marrow that are responsible for producing cells which circulate in the blood, such as red blood cells, white blood cells, and platelets

Where is bone marrow located?

Bone marrow is located in the central cavity inside bones

What are the two types of bone marrow?

• Red bone marrow

• Yellow bone marrow

Which type of bone marrow is more important for the immune system?

Red bone marrow is more important for the immune system than yellow bone marrow

Hematopoiesis

The formation and differentiation of blood cells

What are the main functions of red bone marrow?

• site of hematopoiesis and thus the origin of all immune cells

• site of B-cell development

Where is red and yellow bone marrow found?

Red bone marrow is found within the spongy bone and yellow bone marrow is found in the medullary cavity in the shaft of the bone

What are the main functions of yellow bone marrow?

• Some leukocyte development

• Produces fat and cartilage

How can the organs of the lymphatic system be classified?

The organs of the lymphatic system can be classified by primary or secondary, according to their function in the immune system

Immunocompetent cell

A mature lymphocyte that is capable of recognizing a specific antigen and mediating an immune response

What are the two main primary lymphoid organs and what is their function?

The two main primary lymphoid organs are the thymus and bone marrow, and are the sites of lymphocyte maturation into an immunocompetent cell. Specifically, B-cells mature in the bone marrow and T-cells mature in the thymus.

What are the three main secondary lymphoid organs?

• Spleen

• Lymph Nodes

• MALT (mucosal associated lymphoid tissue)

Effector cells

A mature lymphocyte that has been activated and mediates an immune response against a specific antigen

What is the primary function of secondary lymphoid organs?

The main function of secondary lymphoid organs is their role in being the site of lymphocyte activation into an effector cell through interacting with trapped antigens

How does the immune system discriminate?

Discrimination in the immune system system occurs through the ability of immune cells to distinguish between self and non-self components

What molecule does almost every nucleated cell in the body express at their surface? Why is the molecule important?

Almost every nucleated cell in the body expresses a major historic compatibility complex class I (MHC 1) molecule. This molecule presents a sample of proteins found inside the cell

What class of MHC molecules are present on specialized cells of the immune system, like macrophages and dendritic cells and B cells?

MHC II

How do immune cells use major histocompatibility complexes to discriminate?

Immune cells scan the surface area of the cell, where the MHC is located to recognize if any abnormalities are presented via the MHC protein. If abnormalities are foreign antigens (non-self) Are detected an immune response can be initiated

How does elimination occur in the immune system?

Elimination occurs through the ability of the immune cells to initiate an immune response

What is the overall purpose of the immune system?

The overall purpose of the immune system is to preserve and protect the integrity of the body from environmental agents, such as microbes, chemicals, or abnormal self antigens. This is accomplished by the recognition and response of self and on self

What does the innate immune system consist of and what is its purpose and two main functions?

The innate immune system consists of physical, soluble, and cellular barriers that are scattered throughout the body to prevent the entry of any infectious agents and respond non-specifically. It functions to immediately recognize and respond to invading pathogens with a response within minutes or hours. It also recognizes general patterns not specific for any one antigen, which limits the type of immune response indicated

Does the immune system function as a single unit or separate entities?

The immune system functions as a single unit

What does the adaptive immune system system consist of and what is its purpose?

The adaptive immune system consist of cells and soluble components, capable of recognizing and responding to specific pathogens/antigens

What are the two subdivisions of adaptive immunity?

• Antibody-mediated humoral immunity (mediated by B-cells)

• Cell-mediated immunity (mediated by T-cells)

Which branch of the immune system is considered the first line of defence against foreign agents?

The innate immune system

What is the general time it takes for the innate immune system to recognize and respond to invading pathogens?

A response is generated within minutes or hours

What is a limitation of the innate immune system’s ability to recognize general patterns that are non-specific to antigens?

This limits the type of immune responses that can be initiated

What is the benefit of the adaptive immune system’s ability to respond to specific antigens?

It’s large diversity gives much wider range of responses that can be initiated

How long does it take the adaptive immune system to initiate a response to invading pathogens?

A longer time is required to initiate a response to invading pathogens and typically takes days

What type of memory does the adaptive immune system have and what does this allow for?

The adaptive immune system has immunological memory, which allows for a quick response upon a second infection with the same pathogen

What is the most ancient immune structure found in evolution?

Amebocytes, which are Mobile cells that move like an amoeba in the body of invertebrates.

What do amebocytes move by?

Pseudopodia

What type of cell found in the human immune system today did amebocytes give rise to?

Phagocytes

Which branch of the immune system do phagocytes play a major role in?

The innate immune system

What do phagocytes move by and how do they engulf free pathogens?

Fago sites have the ability to move by pseudopodia and they can engulf free pathogens by phagocytosis

Pseudopodia

Temporary cytoplasm-filled cell membrane protrusions that extend from motile and phagocytosing cells that are used for motility or the ingestion of extracellular components

Phagocytosis

The ingestion of bacteria or other materials by phagocytes and amoeboid protozoans

How is the principle of parsimony seen in the immune system?

Many prominent aspects of the human immune system are recognizable within the immune systems of less complicated species

When making an phylogenic tree, what feature of evolutionary hypothesis is considered best?

The best hypothesis is one that requires the fewest evolutionary changes

What happened to the thymus as the vertebrate immune system evolved?

The thymus was retained in later vertebrates because it remained an important lymphoid organ

What is the evolutionary order of the major lymphoid tissues from earliest to most recent? How often are these lymphoid tissues found in vertebrates?

1. Gut-associated lymphoid tissues (GALT), which are found in almost all vertebrates

2. Thymus and spleen, which are found in some variation of most vertebrates

3. Bone marrow, which not many vertebrates generate lymphocytes in

4. Lymph nodes, which are not found in all vertebrates and are a more recent evolutionary trait

What types of animals are evolutionarily the earliest examples of organisms with B and T cells?

Sharks and rays

Where is the innate immune system found across evolution?

It is found in vertebrates and vertebrates and plants

Why is the fruit fly commonly used as the preferred model organism for biological research?

This is due to its well developed innate immune system

Where is the adaptive immune system found across evolution? Which organisms have a well-developed adaptive immune system?

It is found only in the subphylum vertebrata, which includes all animals with a backbone. Only more complex organisms within this subphylum have a well-developed adaptive immune system.

What major adaptive immune cells are only found in jawed vertebrates?

B cells and T cells

How quickly does the immune system evolve compared to pathogens?

The immune system evolves slowly and continuously while many bacteria and viruses can involve faster

What was the early belief about how pregnancy affected the immune system? How does this differ from recent evidence?

Up until five years ago was theorized that pregnancy damp into the immune system. However, recent evidence suggests that the immune system is in a state of flux during pregnancy where early on, certain cell types in the immune system are activated and recruited to the site of implantation. Subsequently after 12 weeks, the immune system becomes dampened and at the end of pregnancy the immune system becomes less inflammatory.

If immune cells aren’t recruited to the site of implantation during pregnancy, what is the effect?

Without this, implantation cannot be achieved

What type of cell does every immune cell originate from? What process does this occur through?

Every immune cell originates from pluripotent hematopoietic stem cells (HSC) in the fetal liver and the bone marrow. This occurs through the process of hematopoiesis.

Pluripotent

Cells capable of giving rise to several different cell types

What are the two lineages of hematopoiesis?

• Myeloids

• Lymphoids

Where do most of the cells of the innate immune system differentiate from?

Myeloid progenitor cells differentiate into most of the cells of the immune system

What happens when a hematopoietic stem cell commits to the myeloid progenitor lineage?

Only a certain subset of immune cells can evolve

Where do you most of the cells from the adaptive immune system differentiate from?

Lymphoid progenitor cells differentiate into cells that make up most of the adaptive immune system

What are the two major types of lymphoid cells?

B and T cells

What happens once a hematopoietic stem cell commits to the lymphoid progenitor lineage?

Only a certain subset of immune cells can evolve

Where does every blood cell arise from? What does this include?

All blood cells originate from hematopoietic stem cells. This includes erythrocytes (red blood cells), leukocytes (white blood cells), and platelets

What are the two main characteristics of hematopoietic stem cells?

• Self-renewal (has the ability to divide itself to replace “older” cells to keep the pool of stem cells constant)

• Pluripotent/multipotent (can differentiate into several cell types)

What ability does a stem cell lose once it commits to a lineage?

One system cell commits to a lineage, it loses its ability to self renew and becomes a myeloid or a lymphoid progenitor cell

What type of cell generates the majority of cells of the innate immune system?

Myeloid progenitor cells

How many groups of myeloid cells can myeloid progenitor cells differentiate into? What are they and what cells do they include?

Myeloid progenitor cells have the ability to differentiate into four different groups of myeloid cells. Thus being, granulocytes (neutrophils, eosinophils, basophils and mast cells), monocytes (macrophages), erythrocytes (red blood cells) and thrombocytes (platelets)

What processes are platelets a central contributor of? What other purposes do they participate in?

Platelets are a central contributor to the process of coagulation, wound healing, and fibrinolysis. They participate in intervention against microbial threats, recruitment and promotion of innate affect self functions, modulating, antigen presentation, and enhancement of adaptive immune responses

What does new data just about platelets?

New data suggest that platelets have inflammatory functions that can influence both innate and adaptive immune response

Phagocytes

Type of cell capable of phagocytosis that ingests and destroys foreign particles, bacteria, and cell debris

What type of cell are monocytes and macrophages?

Monocytes and macrophages are phagocytes

Where are monocytes located? How are they able to travel outside the circulatory system?

Monocytes are located in the blood and are able to travel outside of the circulatory system by moving across the blood vessel walls

Where are macrophages located?

Macrophages are located in the tissues

What happens when monocytes travel outside the circulatory system and penetrate the tissues? What changes do they undergo?

When monocytes travel outside the circulatory system and penetrate the tissues they become macrophages and undergo changes, where the cell gets bigger, the number and complexity of intracellular structures is increased (pseudopodia, phagosome, or lysosomes) and better phagocytic abilities are acquired