Chapter 1 - Elements of the Immune System and Their Roles

What is humoral immunity?

Humoral immunity is immunity due to antibodies and their actions.

What are humors?

Humors is an old term for body fluids, such as blood or lymph.

What does the common myeloid precursor stem to form?

IT stems to either make granulocyte cells or macrophage cells, OR it stems to make megakaryocytes or erythroid cells.

How do blood lymphocytes respond to lymph borne pathogens?

Infections usually occur in connective tissue where a skin wound occurs. The pathogen itself, the fragments, or the infected dendritic cell is carried to the nearest lymph node by lymphatics.

What is a pathogen?

Any organism that causes disease and includes bacteria, viruses, fungi, and parasites.

What is asplenia?

Asplenia is the condition in which an individual is born without a spleen. This is an immunodeficiency disease, in which the inheritance of one or more mutant genes leads to defects in the immune system's functions. When a person's spleen becomes damaged as a consequence of a traumatic accident or wound, it will often be removed surgically to prevent life-threatening loss of blood into the abdominal cavity. Children who have this procedure, called splenectomy, can be as vulnerable to bacterial infections as asplenic children. For adults, who have already been infected by these pathogens and have developed protective immunity, the consequences of splenectomy are usually slight, but protective vaccination against some pathogens, especially S. pneumoniae, is advised.

How does making something acidic protect us from pathogens?,

By making the areas of growth acidic, the bacteria deter pathogen growth.

What is clonal selection? Clonal expansion?

Clonal selection the mechanism by which immune response derives only from individual antigen specific lymphocytes which are stimulated by antigen to proliferate and differentiate. Clonal expansion is the multiplication of lymphocytes after activation by antigen.

How do commensal organisms enhance human nutrition?

Commensal organisms enhance human digestion because they allow us to digest our food that we normally wouldn't be able to. They also synthesize some vitamins and nutrients for us.

How to commensal organisms protect against disease?

Commensal organisms protect against disease because they physically occupy spatial area and inhibit pathogens to grow in the same space. They also make pathogens compete for resources.

How does the secretion of antibacterial proteins from commensal organisms benefit us?

Commensal organisms that secrete antimicrobial proteins help us because that prevents other bacteria from colonizing in our gut.

What are commensal species?

Commensal species are microbial speceis that live in a healthy human body and occupy a specific niche. They have important functions in the human body.

What are the three main functions of commensal organisms in the human body?

Commensal species in the human body have three main functions: They enhance human nutrition, they protect against disease, and they secrete antibacterial properties.

What are cytokines?

Cytokines are soluble proteins that interact with other cells to trigger the innate immune response.

What are defensins?

Defensins are an antimicrobial substance that has antimicrobial peptides that are secreted by macrophage and neutrophils. They are permeable to the pathogen membrane.

What is a draining lymph node?

Draining lymph node is the lymph node nearest to the site of infection to which extracellular fluid containing antigen and cells from the infection site is transported. Within this lymph node, B cells and T cells with receptors that bind to the pathogen are stimulated to divide and differentiate into effector cells.

Who will participate during infection in the adaptive immune system?

During infection, only those lymphocytes bearing receptors that recognize the infecting pathogen are selected to participate in the adaptive response. They then proliferate and differentiate in order to produce a large number of effector cells specific to that pathogen.

What are eosinophils?

Eosinophils are the second most abundant granulocyte, and their function is to defend against helminth worms and other intestinal parasites. They are large because parasites that attack our system are usually much, much larger than viruses and bacteria.

What are four key elements of the innate immune system?

Four key elements of innate immunity are: pathogen receptors that bind noncovalently to the surfaces of pathogens; proteins such as complement that bond covalently to pathogen surfaces, forming ligands for receptors on phagocytes; phagocytic cells that engulf and kill pathogens; and cytotoxic cells that kill virus-infected cells.

What is the main goal of the immune system?

The main goal of the immune system is to protect the human body from infectious disease.

What are some areas of the body that are mucosal areas?

The respiratory tract, urogenital tract, the gastrointestinal tract, the eyes and mammary glands all produce mucous.

How do B-cells differentiate?

B-cells differentiate into Ab producing plasma cells. This is the only effector function of B-cells.

What is the most important function of antibodies?

The most important function of antibodies is to facilitate the engulfment and destruction of extracellular microorganisms and toxins by phagocytes.

What is a T-cell?

T-cells are only expressed as a cell-surface receptor, never as soluble proteins. Each T cell expresses a single type of T-cell receptor.

What does the granulocyte progenitor entail?

The granulocytes made from this progenitor are neutrophils, eosinophils, and basophils. They have all contain cytoplasmic granules, kill microorganisms, and enhance inflammation. They are also called polymorphonuclear leukocytes.

What is a B-cell?

A B-cell is a small lymphocyte that are plasma cells. They secrete soluble forms of immunoglobulins. These are known as antibodies. Each B cell expresses a single type of immunoglobulin.

What is sa macrophage?

A macrophage is a monocyte that travels in the blood to tissues. Monocytes mature into macrophages, which literally means "large phagocyte." They are long lived and are first to sense an invading microorganism. They then warn other cells by secreting cytokines that recruit nearby neutrophils and other leukocytes.

What is a monocyte?

A monocyte is a leukocyte that circulates in the blood. It is bigger than granulocytes, and have a distinct indented nucleus. They all look the same.

Whats a natural killer cell?

A natural killer cell is a large granular lymphocyte. It is the effector cell of the innate immune system and it's purpose is to defend against viral infections. It does this by entering the infected tissue, by killing the virus infected cells, and by secreting cytokines that impede viral replication in infected cells.

What is sebum?

An antimicrobial substance that contains fatty acids and lactic acids that inhibit bacterial growth on skin.

What is an antigen receptor?

Antigen receptors are surface immunoglobulins and T-cell receptors. Differences in the amino acid sequences of the variable regions of immunoglobulins and T-cell receptors create a vast variety of binding sites that are specific for different antigens and thus for different pathogens. A consequences of this is that the response for one pathogen provides no immunity for another.

What is an antigen?

Any molecule, macromolecule, virus particle, or cell that contains a structure recognized and bound by an immunoglobulin or T-cell receptor is called its corresponding antigen.

What occurs inside a lymph node?

Arriving lymphocytes separate to the T cell or B cell area. Infected dendritic cells (that come and stay) and pathogens enter lymph node via afferent lymphatic vessel. Pathogens are filtered out by macrophages, and germinal centers form by pathogen specific B cells that bind to the pathogen and cause swollen glands.

What is BALT?

BALT is bronchial associated lymphoid tissue, which includes the line respiratory epithelium.

What are basophils?

Basophils are the least abundant granulocyte. They defend against parasites. They are extremely rare so not much is known about them.

How are B-Cells and T-Cells the same? Different?

Both B-cells and T-cells are similarly structured, and both are products of genes that are cut, spliced, and modified. However, each B-cell expresses a single type of Ig, while each T-Cell expresses a single type of T-receptor. Millions of different Igs and TCRs are respresented in a population of small lymphocytes in one human. Adaptive immune responses are made against one pathogen provides no immunity to another.

Where do B-cells and T-cells originate from? Where do they mature?

Both B-cells and T-cells originate from bone marrow. However, they mature in separate places. B-cells mature in the bone marrow, while T-cells migrate in blood from bone marrow and mature in the thymus.

What is the immune system?

Cells in the human body dedicated to defense, which collectively form the immune system.

What are dendritic cells?

Dendritic cells are distinct, star shaped cells that live in tissues that are cellular messengers that are sent to call the adaptive immune response when they are not enough to fight infection. They do this by leaving tissue with intact and degraded pathogens and taking it to lymphoid organs that specialize in making adaptive immune responses.

How does the draining lymph node activate the adaptive immunity?

First, macrophages remove the free pathogens and other debris. Dendritic cells that come stay in lymph node and move to the T-cell areas and stimulate the division and differentiation of pathogen specific small lymphocytes into effector cells. Helper T-cells and cytotoxic-T cells leave the node in the efferent lymph and circulate back in the blood to the site of infection. Other helper T-cells stay and stimulate the division and differentiation of pathogen specific B-cells into plasma cells. Plasma cells then move to the medulla of the lymph node, where they secrete antibodies, which are taken to the site of infection by efferent lymph and blood. Some plasma cells leave node by efferent lymph blood to the bone marrow and continue to secrete antibodies.

What is GALT?

GALT is gut associated lymphoid tissue, which includes: Tonsils, adenoids, appendix, and peyer's patches that line the small intestine.

What is hematopoiesis?

Hematopoiesis is the generation of blood cells. Blood cells are short lived and thus are being continually made. Initially, in the fetus, they are made in the yolk sac. From about 3-5 months, they are being made in the fetal liver and spleen. From about 5 months and onward, they are made in the bone marrow.

What is immunization?

Immunization is a procedure where severe disease is prevented by prior exposure to the infectious agent in a form that can not cause disease.

What is immunological memory?

Immunological memory occurs when some of the lymphocytes selected during an adaptive immune response persist in the body and provide long-term immunological memory of the pathogen. They allow subsequent encounters with the same pathogen to elicit a stronger and faster adaptive response, which terminates infection with minimal illness.

What is immunology?

Immunology is the study of the physiological mechanisms that humans and other aniamals use to defend their bodies from invasion by all sorts of other organisms.

How does the spleen protect against blood borne pathogens?

In the spleen, macrophage and dendritic cells in the spleen phagocytize microorganisms. These cells stimulate B and T cells arriving in the blood. The spleen also has two parts: the red pulp and the white pulp. The red pulp is responsible for monitoring the RBCs and removing them. The white pulp is where WBCs gather and provide adaptive immunity similar to that of the lymph node.

What are inflammatory cells?

Inflammatory cells are white blood cells that are usually present in inflamed tissues and release substances that contribute to inflammation.

What does the adaptive immune response look like?

It has two parts, called the first adaptive immune response and the second adaptive immune response.

What is the Megakaryocyte/Erythroid progenitor entail?

It makes megakaryocytes, which are permanent residents of the bone marrow. They have giant nucleus', as they are the result of the fusion of multiple precursor cells. They also have multiple sets of chromosomes. More importantly, they give rise to platelets, which are membrane enclosed cells with the cytoplasm of megakaryocytes. Their function is to maintain the integrity of blood vessels. They also make erythroblasts, which give rise to red blood cells.

What are lymphatics?

Lymphatics are a network of lymphatic vessels that originate in the connective tissue throughout the body and collect the plasma that continually leaks out of blood vessels and forms the extracellular fluid, called lymph. The lymphatics eventually returns lymph to the blood, chiefly via the thoracic duct, which empties into the left subclavian in the neck. However, lymph is not driven by a dedicated pump and the flow is sluggiesh. The natural movement of the body helps circulate the fluid.

What are lysozymes?

Lysozymes are an antimicrobial substance that attacks the peptidoglycans of pathogens. It is present in tears and saliva and they degrade the bacterial cell wall.

What is MALT?

MALT is mucosal associated lymphoid tissue. Pathogens arrive by direct delivery across mucosa mediated by specialized cells of the mucosal epithelium, called M cells. Lymphocytes enter tissue from the blood and if not activated, they will leave the lymphatics. Activated lymphocytes stay within the mucosal system. By having direct contact, the interaction can be almost immediate which can be very useful when combating pathogens.

Possible essay question: **How does a macrophage respond to a pathogen?**

Macrophages respond to pathogens by using different receptors to stimulate phagocytosis and cytokine secretion. The left panel shows receptor-mediated phagocytosis of bacteria by a macrophage. The bacterium (red) binds to cell-surface receptors (blue) on the macrophage, inducing engulfment of the bacterium into an internal vesicle called a phagosome within the macrophage cytoplasm. Fusion of the phagosome with lysosomes forms an acidic vesicle called a phagolysosome, which contains toxic small molecules and hydrolytic enzymes that kill and degrade the bacterium. The right panel shows how a bacterial component binding to a different type of cellsurface receptor sends a signal to the macrophage's nucleus that initiates the transcription of genes for inflammatory cytokines. The cytokines are synthesized in the cytoplasm and secreted into the extracellular fluid.

What are mast cells?

Mast cells are granular cells that are like basophils. They are found in all connective tissues, but their progenitor remains unknown. Their activation and degranulation is a major contributor to inflammation.

Describe the lymphocyte recirculation.

Mature B and T cells move freely through the blood and in the lymph. They usually leave the primary lymph tissue where they are developed and enter the blood. When they reach capillaries, they leave blood and enter the lymph nodes. If a lymphocyte becomes activated by a pathogen, it remains in the lymph node; otherwise it will be returned to the blood.

What is neutralization?

Neutralization occurs when an antibody binds to a pathogen such that it inhibits pathogen growth, replication, or interaction with human cells.

What are neutrophils?

Neutrophils are the most abundant granulocyte. They are responsible for capturing, engulfing, and killing microorganisms. They are the effector cells of the innate immune system. In other words, they are the first responders. Macrophages call for support and they are the first to arrive on scene. However, they are short lived and die at the site of infection.

What is opsonization?

Opsonization is the phenomenon by which a coating of antibody facilitates phagocytosis.

What is immunity?

People or animals who are unaffected by a foreign pathogen.

What are primary lymphoid tissue?

Primary lymphoid tissue are bone marrow and thymus.

What are some antimicrobial substances that are secreted by epithelial surfaces?

Sebum, defensins, lysozymes, and things that make the surface have an acidic pH.

What are secondary lymphoid tissue?

Secondary lymphoid tissue are tissue that are not bone marrow or thymus.

What are some examples of physical and chemical barriers?

Skin and mucous membranes are two examples. The skin provides a physical barrier of epithelium which is protected by keratinized cells. Mucosal surfaces or mucosa secrete mucous that trap pathogens and keep them from spreading.

What are some secondary lymph tissue?

Some examples of secondary lymph tissue are: GALT, BALT, MALT.

What are some of the benefits of the adaptive immune response?

The adaptive immune system has increased power and focus of the immune system (this is done via white blood cells called lymphocytes). It adapts to specific pathogens, it is long lasting, and it is evolved only in vertebrates.

What is acquired immunity? Protective immunity?

The adaptive immunity provided by immunological memory is also called acquired immunity or protective immunity

What is the benefit of inflammation?

The benefit to the discomfort and disfigurement caused by inflammation is that it enables cells and molecules of the immune system to be brought rapidly and in large numbers into the infected tissue.

What are leukocytes?

The cells of the immune system are principally the white blood cells, called leukocytes, and the tissues being related to them.

Explain an example in which taking antibiotics can be detrimental.

The colon is usually colonized by a large numbers of commensal bacteria. However, sometimes antibiotics will kill these off in great numbers. Then, pathogenic bacteria gain a foothold and produce toxins that cause mucosal injury. Red and white blood cells later leak into the gut between the injured epithelial cells.

What does the common lymphoid precursor stem to form?

The common lymphoid precursor stems off to make NK cells, B-cells, and T-cells.

What are some differences in the innate vs the adaptive immune system?

The effector mechanisms used in the adaptive immune response are similar to those used in the innate immune response; the important difference is in the way in which lymphocytes recognize pathogens. The innate immunity has receptors that recognize features shared by groups of pathogens and are not specific. In contrast, lymphocytes recognize pathogens by using cell-surface receptors of just one molecular type. This means the adaptive immune response can be made specific for a particular pathogen.

What are some areas of the body that have physical barriers?

The epithelium, or the outside skin, is an example of a physical barrier.

What is the first adaptive immune response? What does it do?

The first adaptive immune response is called the primary immune response. It occurs when you first encounter a pathogen you've never encountered before. The body will take a while to create a response to it, but once it does, it is stored in immunological memory.

What is the first line of defense?

The first line of defense is the innate immune system, which includes physical and chemical barriers to infection, and responses that are ready and waiting to halt infections before they can barely start.

Give a general overview of the immune system. Try to describe both systems.

The first part of the immune system is the innate immune system. It creates a physical and chemical barrier. There are responses ready and waiting for infection. The second part of the immune system is the adaptive immune system, which only activates only after the innate immune system fails.

What happens if a human lacks the innate system? What happens if they lack the adaptive immune system?

The innate immune system is required in order to activate the adaptive response system. If you do not have this, the lack of adaptive response can lead to failure to clear the infection. This is why much of medicine is concerned with small proportion of infections that innate system fails to terminate. Much of what we know comes from studying when it fails.

What does the lymphoid progenitor entail?

The lymphoid progenitor is responsible for making large granular lymphocytes and small granular lymphocytes.

What does the macrophage and dendritic cell precursor entail?

The macrophage and dendritic cell precursor makes monocytes, macrophages, and dendritic cells.

What are the major lymphoid organs?

The major lymphoid organs are: bone marrow, thymus, spleen, adenoids, tonsils, appendix, lymph nodes, and Peyer's patches.

What causes inflammation?

The overall effect of the innate immune response is to produce inflammation. Cytokines induce local dilation of blood capillaries, which increases blood flow causing the skin to warm and redden. Vascular dilation introduces gaps between the cells of the endothelium, which is also changed by cytokines, inviting white blood cells to attach to it and move from the blood into the inflamed tissue.

What is the second adaptive immune response do?

The second adaptive immune response is a secondary immune response. It occurs after a pathogen has already encountered and there is immunological memory for it. It makes for a stronger, faster response and stops infection with minimal illness.

What is the second line of defense?

The second line of defense is the adaptive immune system. If the innate system fails, the adaptive system will take time to develop resistance and specificity to a pathogen, but will be more effective.

How do T-cells differentiate?

There are two main effector functions of activated T-cells. The first is cytotoxic T-cells, which kill cells. They are similar to the NK cells; except NK cells are part of the innate immune system and cytotoxic T cells are part of the adaptive system. They can also differentiate into helper t\T-cells, which are present in order for other cells in the immune system to do their job. For example, they can: secrete cytokines that help other cells become fully activated effector cells, help macrophage be more active in phagocytosis, help B-cells become plasma cells, and help control the activity of other T-cells (regulatory T-cells).

Briefly describe how the innate immune system responds to breached barriers.

There are two parts to the innate system. The first step is to recognize that the pathogen is present. There are soluble proteins found in our blood and cell surface receptors that allow us to do so. Then, after they recognize that there is a pathogen present, the next step is to recruit destructive effector mechanisms that kill and eliminate pathogens. Effector mechanisms are provided by effector cells, and a battery of serum proteins called complement that help the effector cells by marking pathogens with molecular flags and attacking them.

What are hematopoietic cells?

They are collective and include white blood cells, red blood cells, and megakaryocytes. They all start with a hematopoietic stem cell and branch off from there.

Why is the spleen so important to the immune system?

We know that lymphocytes enter and leave the spleen in the blood, not in lymph. Therefore, pathogens that enter through the blood are filtered by the spleen. The spleen is responsible for filtering out damaged or old RBCs. They are also responsible for defending against blood born pathogens.