Chapter 1
1. Can you explain what is the difference between humoral and cellular immunity?
The difference between humoral and cellular immunity is that humoral immunity secretes
antibodies to fight against antigens, it is quick in reaction against antigen. While cellular
immunity secretes cytokines to attack the pathogens, it shows delay though permanent
action against pathogens.
- Cellular immunity: T-cells will destroy infected cells. Person is exposed to pathogen.
Pathogen enters/infects body cell. Antigens of pathogen are displayed on infected cells.
Phagocyte swallows and destroys pathogen. Phagocyte displays the antigen of the
pathogen. Inactivated t-cells bind to the antigen-displaying phagocyte. Proteins will
activate the T-cell and it will divide into:
o Memory t-cells: to fight pathogens in the future.
o Active (plasma) t-cells: bind to the infected body cell and release proteins and
enzymes to destroy the infected cells.
- Humoral immunity: B-cells produce antibodies. Person exposed to a pathogen.
Membrane-bound antibodies of a B-cell will bind to the pathogen. Pathogen eaten by B-
cell and broken down. Antigen of pathogen will be displayed on the B-cells. Helper T-cells
binds to antigen-presenting B-cell. Protein activate B-cell. B-cell divides into:
o Memory B-cell: to fight pathogens in the future.
o Active B-cells: produce antibodies to attach to pathogen.
Phagocyte swallows pathogens and breaks it down.
2. Why is it important to have both an innate and adaptive response? What are the
differences?
It is important to have both an innate and adaptive response to give the human body full
protection. Innate responses (macrophages, neutrophils and NK cells) are rapid responses
(hours), are fixed, have a limited number of specificity and are constant during response. It is
already present in the body while the adaptive response is created in response to exposure
to a foreign substance. The adaptive response (T&B lymphocytes) is much slower (days-
weeks), it is variable, has numerous highly selective specifications and improves during
response.
- Innate response: causes inflammation at sites of infection. Phagocytosis of bacteria
(bacteria are eaten), signaling by secretion of soluble proteins (cytokines) to induce
vasodilation via activation of endothelium (which causes warm and red skin).
Vasodilation induces gaps in the endothelium which makes it permeable and blood
plasma flows into the connective tissue, causing edema. 1)pathogen recognition. 2)
recruitment of destructive effector mechanism (macrophages and neutrophils; recognize
many different types of cells) to attack pathogen by phagocytosis.
- Adaptive response: can be made specific for a particular pathogen by using only those
lymphocytes receptors that bind to the infecting pathogen by cell-surface receptors.
Relies on clonal selection and expansion which is proliferation and differentiation into
lymphocytes. T and B cells with TRC and BRC. Effector lymphocytes help eliminate
pathogen. Memory lymphocytes for immunological memory.
3. What is the difference between chemokines and cytokines?
Immune cells secrete and react to the soluble proteins cytokines and chemokines, they bind
cyto- and chemokines via specific receptors expressed on their cell surface. Cytokines induce
cell division and activation (can occur via autocrine or paracrine), chemokines induce
migration. Cytokine is a general term used for all signaling molecules while chemokines are
specific cytokines that function by attracting cells to sites of infection/inflammation.
, 4. Do you know which cells belong to the innate and which to the adaptive immune
response?
Cytokines trigger the innate immune response; they induce dilation of the blood vessels to
increase the blood flow causing a warm and red skin. The vasodilation itself causes gaps in
the endothelium so it becomes permeable and blood plasma goes into the connective tissue,
causing thick edema. Cytokines also change the adhesive properties of the vascular
endothelium, inviting white blood cells to attach to it and move from the blood into the
inflamed tissue. Chemokines control the release of innate immune cells from the bone
marrow during homeostasis as well as response to infection and inflammation.
5. Can you describe the process of clonal expansion and for which cells this is important?
Clonal expansion is the process where daughter cells arise from a parent cell. It is important
for long-term B-lymphocytes that have a long memory to keep renewing the cells so it can
recognize pathogens for a long time.
6. Can you describe where the diversity of immune cells originates from and what the
differences are of lymphoid and myeloid precursors?
Hematopoiesis cells are leukocytes, megakaryocytes, red blood cells and their progenitor
cells. The cells can mature and commit into one of the three cell-lines; erythroid, myeloid and
lymphoid. The differences between lymphoid and myeloid are that lymphoid refers to lymph
and the lymphatic system containing B&T cells, NK cells and lymphoid innate cells. Myeloid
comes from bone marrow and red blood cells, such as macrophages neutrophils, basophils
etc.
7. Do you know what is the difference between primary and secondary lymphoid organs?
The primary lymphoid organs take care of leukocyte development and the secondary
lymphoid organs take care of filtering lymphatics and cells coming from tissues, and
pathogen recognition by adaptive immune system.
- Primary lymphoid organs: B-cells are generated in the bone marrow and the T-cells are
generated in the thymus.
- Secondary lymphoid organs: activation of the B&T-cells by filtering the lymph fluid from
the tissues.
8. Do you understand how lymph and blood are connected and connect to secondary
lymphoid organs?
T and B lymphocytes come from the heart via an artery into the lymph node, then leave it via
the lymph tube. B and T cells enter lymph node via afferent lymphatic, stay in the T-cell area
or the germinal center, and leave via the efferent lymphatics into the blood vessels, via the
blood into secondary lymphoid organs.
9. What does the term opsonization mean and when is it important and what is the process?
Opsonization is the process where microbes are coated with host-produced proteins and
lipids, to let the opsonized bacterium bind to the receptors on the phagocyte, important to
make it easier for the phagocyte.
10. Can you describe the structure of a secondary lymphoid organs and its regions?
Secondary lymphoid organs are kidney-shaped, located at junctions in the lymphatic system
where are more afferent than efferent lymph. It is composed of a cortex and a medulla.
Chapter 2
The type of immune response depends on the type of infections that are produces, intracellular (kill
human cells to get rid of the pathogens) or extracellular (accessible to soluble proteins to get rid of
the pathogens).
- Intracellular: can be handled by NK cells of the innate immune system or the cytotoxic T cells
of the adaptive immune system.
- Extracellular: can be handled by proteins that can stick to them, like the complement system
in the innate immune response, and antibodies that are produced by the B-cells in the
adaptive immune system.
, 1. Why are barriers important?
Barriers are important to keep pathogens from entering the human body. The first barrier is
epithelium with organized tight junctions. It is important to protect the mucus layer from
incoming pathogens. Barriers consist of three components;
- Mechanical; such as tight junctions, tears, mucus movement or air and fluid flow.
- Chemical; such as FA, PH, enzymes and peptides.
- Microbiological; such as normal microbiota
2. What is the complement activation?
Complement is the plasma proteins of the soluble molecules during innate immune
response. Complement coats the surface of bacteria or extracellular fluids to make is easier
to get phagocytosed. The inactive form is called zymogen. Complement activation is the
activation of the complement triggered by infection, which proceeds by a cascade of
enzymatic reactions. Each protease cleaves and activates the next protease in line.
What is complement fixation?
Complement fixation is fixation of a complement to a pathogen, for example C3 splits into
C3b and C3a. C3b binds to the surface of the pathogen. Complement fixation happens in
order to make sure the pathogen can be degraded by phagocytes and organize protein
complexes that damage the pathogens membrane.
3. Can you describe C3 and its function?
C3 is the most important complement, lacking C3 causes severe infections. C3b goes into
complement fixation as described above and C3a acts as a chemoattractant to recruit
effector cells, such as phagocytes, from the blood to the infection sites. C3 has a high energy
thioester bond, when C3 splits, the bon becomes available for nucleophilic attacks by water.
4. Can you describe the 3 complement activation pathways?
- Alternative pathway of complement activation: the pathway that works at the start of
infection, it creates an environment where C3 can be cleaved.
o Activated by spontaneous activation by the pathogen (hydrolysis).
- Lectin pathway of complement activation: part of the innate immunity but is induced by
infection and requires some time to regain its strength. Mannose-binding lectin binds to
pathogen surface. Circulates plasma and cleaves C2 and C4 into C3, and cleaves that into
C3a and C3b.
o Activates by carbohydrate recognition.
- Classical pathway of complement activation: part of both innate and adaptive immunity.
Requires binding of either an antibody or an innate immune system protein called C-
reactive protein (binds phosphocholine, 1000x more present in plasma during acute
phase of infection) to a pathogens surface. Activation and cleavage of C2 and C4 into C3
convertase, with help of C1. When this bond is there, C3 is activated and cleaved.
o Activation by IgM antibodies.
5. Why is the liver important in the complement activation?
The liver produces mannose-binding lectin which is needed in the lectin pathway of
complement activation. The liver also produces C-reactive protein which is needed in the
innate immune response in the classical pathway of complement activation.
6. What is MAC, MBL and CRP?
CRP is C-reactive protein, active during the classical pathway of complement activation of
innate immunity. MBL is mannose-binding lectin present during the lectin pathway of
complement activation of the innate immunity. MAC is membrane attack complex, that
induce pore formation in the bacterial membrane leading to lysis.
Chapter 3
1. What is the difference between recognition of self and non-self, which cells and receptors
are involved?
