Cells And Organs

Question 1

Origin of immune system cells

Answer 1

Hematopoietic stem cells which are self renewing

Two branches: Myeloid progenitor and Lymphoid progenitor

myeloid: dendritic cells, granulocytes, eosinophils, basophils, megakaryocyte, erythrocyte

Lymphoid: NKC, b-cell, t-cell, dendritic cell

Question 2

Two arms of immune defense

Answer 2

Innate and adaptive

Question 3

Innate immunity

Answer 3

First line
Skin, cousin, membranes, chemicals

Second line
Phagocytosis, complement, interferon, inflammation, fever

Question 4

Adaptive immunity

Answer 4

Third line

Lymphocytes, antibodies

Question 5

Cells of innate immunity- first response

Answer 5

Granulocytes OR polymorphonuclear leukocytes are a subgroup of white blood cells characterized by the presence of cytoplasmic granules

They are produced in the bone marrow

Are classified as basophils, eosinophils, or neutrophils

They are named as such because of their distinct staining characteristics using hematoxylin and eosin histology always preparations

Question 6

Basophils

Answer 6

Granules in basophils stain dark blue
Important for host defense against parasites and may be involved in allergic and inflammatory responses
Basophils contain toxic granules which are used to destroy pathogens during the process of phagocytosis
Basophils express several adhesion molecules which play a critical role in their circulation, including LFA-1 (CD11a/CD18), MAC-1 (CD11b/CD18) and CD44

Question 7

Eosinophils

Answer 7

Stain bright red
Differentiate from myeloid precursor cells in response to IL-3, IL-5 and GM-CSF
Important for host defense against parasites and may be involved in allergic reactions
Respond to chemokines such as CCL5/RANTES, CCL11/eotaxin-1, and CCL24/eotaxin-2secreted by neutrophils or lymphocytes
Recruited eosinophils release the toxic substances contained in their granules to destroy pathogens and fight infection

Question 8

Neutrophils

Answer 8

Stain neutral pink
The most numerous innate immune cell (50-70% of all white blood cells)
Immature neutrophils have a distract band-shaped nucleus which changes into a segmented nucleus following maturation
They circulate in the bloodstream looking for foreign objects to phagocytose and degrade
Number of circulating neutrophils is estimated using the absolute neutrophils count (ANC)

Question 9

ANC

Answer 9

May be high (neutrophilia) due to kidney failure or bacterial infection

Leukemia or bone marrow damage results in a lower number of neutrophils (neutropenia) and an increased risk of infection

Question 10

Granulocytes at work

Answer 10

Can be identified by expression of CD16, CD34 (immature state) and CD11b/CD18 (activated state)

Additionally, activated basophils can be identified by CD13/Aminopeptidase N, CD107a/LAMP1 or CD164; eosinophils by CD44, CD69, IL-5, and neutrophils by CD16, L-selection (CD62L)

Question 11

Mast cells

Answer 11

Generated by bone marrow
Mast cells are similar to basophils leukocytes
They have a common progenitor (CD34+ precursor cells)
There are two types of mast cells:
-connective tissue mast cells — local allergic reaction
-mucosal mast cells, which are found in areas of the body that are exposed to the external environment (lung mucosa, digestive tract, mouth and nose)

Defense against parasites
Mast cells found in tissues can mediate allergic reactions by releasing inflammatory mediators like histamine

Question 12

Monocytes/Macrophages

Answer 12

They are found in the bloodstream and in tissues
Monocytes circulate in the peripheral blood before entering tissues to replenish tissue-specific macrophage populations (osteoclasts, microglia cells, histiocytes, and Kupffer cells)
Macrophage, big eater, named for their ability to ingest and degrade bacteria

Upon activation, monocytes and macrophages coordinate an immune response by notifying other immune cells of existing infection
Macrophages can present antigens to lymphocytes
Macrophages also have important non-immune functions, such as recycling dead cells, like red blood cells
These housekeeping functions occur without activation of an immune response

Question 13

Natural killer cells

Answer 13

Innate immune cells
Certain sub populations of NK cells have features of both innate and adaptive immunity (NKT cells)
They recognize and kill virus-infected cells or tumor cells
They contain granules, which are filled with proteins that can form hole in the target cell and also cause apoptosis
Besides their function as cytolytic effectors they are also regulators of immune response

Question 14

Dendritic cells

Answer 14

Specialized sentinel cells that constantly sense and respond to their immediate environment
All DCs are hematopoietic bone marrow-derived cells, although they undergo maturation in either, the bone marrow, lymphoid, or non-lymphoid tissues

DCs capture, process, and present antigens to T cells and thus are crucial for bridging innate and adaptive immunity as well as promoting self-tolerance
Upon exposure and uptake of pathogens, maturing DCs travel to secondary lymphoid organs where they become potent T cell activators
DCs are classified as, classical/conventional dendritic cells (cDCs) and plasmacytoid dendritic cells (pDCs)
pDCs have the ability to secrete large amounts of type I interferons upon activation through TLR7 and TLR9

Question 15

B lymphocytes

Answer 15

Humoral immune response
Mature in the bone marrow or bursa of birds
Activated when they bind antigens through their receptors (BCR)
Responsible for generating antibodies to specific antigens

Antibodies coat the surface of a pathogen and Steve three major roles: neutralization, opsonization, and complement activation

Question 16

Neutralization

Answer 16

Occurs when the pathogen is covered in antibodies and cannot further infect host cells

Question 17

Opsonization

Answer 17

An antibody-bound pathogen serves to alert immune cells such as neutrophils and macrophages, to engulf and digest he pathogen

Question 18

Complement activation

Answer 18

Process for directly destroying or losing pathogens
Some complement components act as opsonins— can opsonize pathogens

Bond to antibodies, cascade, holes in cell membrane created

Question 19

T lymphocytes

Answer 19

Express an antigen specific receptor TCR
They begin as thymocytes (precursors to T cells) and end as lymphocytes
Thymocytes develop from hematopoietic stem cells in the bone marrow and then move to mature in the thymus
They undergo several stages of selection and quality control to ensure that maturation results in functional T cells

Essential component of cellular immune response
Divided into two broad categories: CD8+ T cells and CD4+ T cells based in which co-receptor protein is present on the cell surface
CD8+ T cells also are called cytotoxic T cells or cytotoxic T lymphocytes (CTLs)

Recognize and kill infected or cancer cells
CTLs have cytotoxic granules, containing cytotoxic that kill target cells

Question 20

CD4+ T cell subsets

Answer 20

Th1
Th2
Th17
T regulatory cells

Question 21

Th1

Answer 21

Coordinate immune espouses against intracellular pathogens
They produce and secrete molecules (cytokines) that alert and activate other immune cells, like bacteria-ingesting macrophages

Question 22

Th2

Answer 22

Coordinate immune responses against extra cellular pathogens, like helminths (parasitic worms), by alerting B cells, granulocytes, and mast cells

Question 23

Th17

Answer 23

Named for their ability to produce interleukin 17 (IL-17) a signaling molecule that activated immune and non-immune cells

Protect surfaces (skin, guy) against extra cellular bacteria (recruitment of neutrophils)

Question 24

Regulatory T cells (Tregs)

Answer 24

Monitor and inhibit the activity of other T cells

Question 25

Communication of immune cells

Answer 25

Immune cells communicate in a number of ways, either by cell-to-cell contact or through secreted signaling molecules
Receptors and ligands are fundamental for cellular communication
Receptors are protein structures that may be expressed on the surface of a cell or in intracellular compartments
The molecules that activate receptors are called ligands, which may be free-floating or membrane-bound
By altering the expression and density of various receptors and ligands, immune cells can dispatch specific instructions tailored to the situation at hand

Question 26

Molecules involved in immune cell communication

Answer 26

Cytokines
Toll-like receptors 
B-cell and T-cell receptors
Major histocompatability complex (MHC)
Complement

Question 27

Cytokines

Answer 27

Small proteins with diverse function such as cell growth, activation, etc

Question 28

Toll-like receptors

Answer 28

Expressed on innate immune cells, like macrophages and dendritic cells
TLRs recognize general microbial patterns and they are essential for innate immune-cell activation and inflammatory responses

Question 29

B and T cell receptors

Answer 29

Expressed on B cell and T cells.

Recognize foreign antigens

Question 30

Major histocompatibility complex

Answer 30

MHC proteins function as carriers to present antigens on cell surfaces
Also signal whether a cell is a host cell or a foreign cell

Question 31

Complement

Answer 31

Particularly C3a and C5a
Consists of a series of proteins found in blood
Punches small holes into the pathogen, creating leaks that lead to cell death
Also serve as signaling molecules that sort immune cells and recruit them to inflammatory sites

Question 32

Organs of the immune system

Answer 32

Lymphoid cells are first produced in the yolk sac, fetal one yum, and liver
In older fetuses and adults, lymphoid cells are mainly produced in bone marrow

Bone marrow is a hematopoietic organ that gives rise to all blood cells

Question 33

Types of lymphoid organs

Answer 33

Primary: bone marrow, thymus, bursa of fabricius
Secondary: spleen, lymph nodes, non-encapsulated lymphoid tissue, peyer’s patches

Question 34

Primary lymphoid organs

Answer 34

Organs that regulate the development of lymphocytes

T lymphocytes develop in bone marrow and mature in the thymus

B lymphocytes develop and mature in different primary lymphoid organs depending on species
Bursa in birds
Bone marrow in primates and rodents
Intestinal lymphoid tissue in rabbits, dogs, ruminants, and pigs

Primary lymphoid organs are usually not sites of lymphocyte interaction with microbial antigens

Question 35

Thymus

Answer 35

Located in the thoracic cavity in front and below the heart
Large in newborns but small to invisible in adult animals-undergoes involution

Covered by a connective tissue capsule and consists of lobules
The outer part of each lobule, called the cortex contains thymocytes
The inner part of the lobule,medulla contains only few lymphocytes
No lymphatic vessels leave the thymus

Question 36

Thymus function

Answer 36

Function: maturation of T lymphocytes
T lymphocytes learn to recognize self antigens
Thymocytes with receptors that bind strongly to self antigens are destroyed through a process called apoptosis
Thymocytes that cannot bind any MHC II molecules are also removed
Thymocytes that recognize MHC II/Ag complexes with moderate affinity are allowed to live- positive
The positively selected cells leave the thymus as mature T lymphocytes and populate the secondary lymphoid organs
The maturation process is highly regulated by a mixture of cytokines and thymic hormones such as thymosins, thymopoietins, thymulin, and thymostimulins

Question 37

Bursa of fabricius

Answer 37

In birds only
Round sac located just before the cloaca
Like the thymus- undergoes involution

Epithelium embed the lymphocytes and lines a hollow sac connected to the cloaca by a duct
Epithelium makes folds that extend into the sac called follicles
Each follicle has a cortex and medulla
The cortex contains lymphocytes, plasma cells, and macrophages

Question 38

Bursa function

Answer 38

Maturation of B lymphocytes
Negative and positive selection of B lymphocytes
Differentiation of antibody-forming cells

Question 39

Secondary lymphoid organs

Answer 39

Divided into:
Encapsulated organs: lymph nodes, spleen
Non-encapsulated tissue: mucosal lymphoid organs

They develop late in fetal life and persist in adult life
Enlarge in response to antigenic stimulation
Surgical removal does not impair immune capability
They contain dendritic cells which trap and process antigens, and later present these antigens to lymphocytes to initiate an adaptive immune response

Question 40

Lymph nodes

Answer 40

Round shaped or bean shaped encapsulated organ
Act as filters of lymph to trap antigens
Contain two important regions: outer cortex and inner medulla, between these two is the paracortex
B lymphocytes are found in the cortex in germinal centers surrounded by capsules
T cells and DCs are mainly found in the paracortex
The medulla contains mainly different types of cells

Afferent lymph flows into the node from local tissue and carries lymphocytes, DCs and antigens
Lymph enters the subcapsular sinus and then percolates through the node to the medullary sinus
Lymph exits through the efferent lymphatic vessel
Lymph nodes have arterial and venous blood supply

Principle function is to facilitate the interaction between dendritic cells and antigen sensitive T and B lymphocytes

Question 41

Spleen

Answer 41

A large encapsulated organ found in almost all vertebrate animals
Structured by a network of connective tissue trabeculae
Structural differences exist between animals (non-sinusal spleen in cats)

Consists of two types of tissue:
—red pulp: blood filtering and RBC storage
—white pulp: where immune induction occurs, rich in lymphocytes
Primary immune function: filters blood for blood-borne antigens, cellular debris, and aged blood cells
Stores RBCs, platelets, recycles iron

Question 42

Peyer’s patches

Answer 42

Non-encapsulated lymphoid tissue located in the wall of the small intestines
In ruminants, pigs, dogs, and rabbits- PP are found in the ileum = primary lymphoid organ for B cell development
In young ruminants the PP may be as long as two meters
Contain densely packed lymphoid follicles containing only B lymphocytes

Covered by an epithelial layer containing specialized cells called M cells which have characteristic membrane ruffles

Undergo involution
In rabbits and rodents- PP are located at random intervals in the ileum and juju I’m
In rabbits and rodents PP develop 2-4 weeks after birth and do not undergo involution

Function similar to bursa

Question 43

Non-encapsulated lymphoid aggregates

Answer 43

Scattered throughout the muscosal surfaces of the body
Makes up a large portion of the total lymphoid tissue
Mostly located in the intestinal mucosal
Generally called mucosal-associated lymphoid tissue (MALT) which includes:
Gastrointestinal (GALT): best known MALT. It is inductive site of intestinal immune response and effector site of intestinal immune response
Bronchial p (BALT)
Nasal (NALT)
Conjunctiva (CLAT)