Immune System & Lymphoid Organs Flashcards
Innate immunity
Immediate, nonspecific actions.
Skin, mucus, neutrophils, NK cells, macrophages, and other leukocytes producing antimicrobial chemicals (HCl, defensins, lysozymes, complements, interferons)
How do macrophages in the innate immune system know when a bacterium is out there?
toll-like receptors recognize common invader patterns (structurally conserved molecules from microbes)
What are the 3 funcitons of macrophages in general again?
PIcks up debris
Eats invaders and presents antigens to the B cell
Non-specific phagocytosis to kill
Cell lineage of macrophages
Hematopoietic stem cells
> Common myeloid progenitor
> Progenitor cells
> Monoblasts
> Monocytes
> Macrophage
Neutrophils in the innate immune system
are ready in the blood, waiting to kill
(don’t present antigens)
How do natural killer cells kill?
Produce cytokines
Force infected cells into apoptosis
(Like neutrophils, they’re also just waiting in the blood to kill)
Adaptive/acquired immunity
Acquired gradually by exposure; more specific; slower
- B & T lymphocytes activated against specific invaders when they are presented with specific molecules by antigen-presenting cells (APC)
- Produces memory lymphocytes so a similar response can be mounted rapidly if the invader appears again
B cells make antibodies. Which part of an antibody binds to antigens?
Which part binds the cell receptor?
Fab binds antigen
Fc binds cell receptor (and determines Ab’s class)
What are the 5 types of antibodies B cells make?
IgG
IgA
IgD
IgE
IgM
Clonal selection
- Stem cells differentiate into antigenically committed B cells in the bone marrow
- B-cells move to peripheral lymph tissue and contact their antigen
-
Rapid proliferation into memory cells & plasma cells (forms germinal center)
- Plasma cells create antibodies for greater immune response
- Memory cells circulate and allow an even faster immune response if the antigen is encountered again
2 main mechanisms antibodies work by
*Opsonization: receptors on leukocytes bind antibodies that are already attached to the antigens of microorganisms, thus increasing the efficiency of phagocytosis.
*Neutralization: antibody covers viruses outside the cell so it can’t enter one
B cells differentiated in bone marrow; T cells differentiate ____
B cells secrete its receptors for antibodies; T cells’ receptors ____
B cells can recognize an antigen by itself; T cells recognize antigens if ____
T cells mature in the thymus
T cell receptors remain on its surface
T cells recognize antigens if properly presented
3 types of T cells: CTLs, Helper, and Regulatory
-
Killer T cells/Cytotoxic lymphocytes (CTL): they attach to cell sources of antigens on foreign or virus-infected cells and trigger apoptosis.
- Has CD8 coreceptors for MHC class I molecules
- Similar to NK cells
-
Helper T cells (Th cells):
- Has CD4 coreceptors for MHC class II molecules
- Produces cytokines that promote differentiation of B cells into plasma cells
- Activates macrophages & CTLs
- Induce inflammation
- Can become memory helper T cells
- Regulatory/Suppressor T cells inhibit immune response & maintain unresponsiveness to self-antigens
-
T cell diversity is generated by
gene segment recombination
Major histocompatibility complex proteins (MHCs)
- MHC I proteins are displayed as “non-self” peptides on infected or mutated cells to alert killer T cells that they need assisted suicide
-
MHC II proteins displayed on the cell surface w/antigens by APCs to inform helper T cells to activate immmune response
- these MHCs display peptides from whatever the cell ingested
Adaptive immune response
- Antigen-presenting cell ingests antigen and displays on its MHC II
-
Helper T cell (Th) bind MHC II and becomes activated to secrete interleukins that promote both Tc & Th cell proliferation & differentiation
- “MHCII-restricted”
Cellular Immunity: Tc cells are activated by antigen-MHC I complex (“MHC I restricted”) expressed on infected cells to differentiate into memory & CTL cells.
Humoral immunity: Th cell activate B cells to proliferate into plasma & B memory cells
Humoral immunity purpose
antibody production
cellular immunity purpose
killing virally infected cells
Lymphocytes vs Accessory cells
- lymphocytes
- B cells
- T cells
- NK cells
- Accessory cells (antigen-presenting cells)
- Macrophages
- Dendritic cells
- Follicular dendritic cells
Both T & B cells are derived from the ___, but differentiate in different places.
bone marrow
Macrophages & dendritic cells are both derived from ____ and both present antigens, but which one is phagocytic?
Both are from monocytes
Macrophages are phagocytic
Follicular dendritic cells are derived where?
Lymph nodes
(mesenchymal origin, not bone marrow)
What are the two supporting cells of lymphoid organs?
- Reticular cells: create a meshwork of reticular fibers (collagen type III)
-
Thymic epithelial cells (TECs)/ Epithelioreticular cells support the thymus
- Note: no reticular fibers in the thymus!
- Origin is epithelial.
The primary lymphatic organs are ____
The secondary lymphatic organs are ___
Primary: bone marrow & thymus
Secondary: tonsil, spleen, lymph nodes, lymphatic nodules
Structure of the thymus
- Connective tissue apsule & septa divide it into lobules
- Cortex and medulla
- Cells:
- T lymphocytes
- Epithelioreticular fibers
- Macrophages
No lymphatic nodules or reticular fibers; more basophilic
Process of lymphoid stem cells developing into immunocompetent stem cells in the thymus
- T cell begins with nothing and passes through ERC1 to enter the cortex.
- No Tcell receptor, CD4 (for Th), or CD8 (for Tk)
- Enters the cortex and ERC2 puts TCR, CD8, & CD4 on it
- Pass through ECR3 & 4 to enter the medulla.
- ERC5 takes off either their CD4 (become Tk) or losing their CD8 (bcoming a Th)
ERC6 (Hassall’s corpuscle) has no function but is structurally distinct for thymus medulla.
Blood thymic barrier- purpose and layers (inner to outer)
creates an antigen-free environment so T cells can mature without beign activated or proliferating.
- Endothelial cell of continuous capillary
- Basal lamina of endothelial cell
- Connective tissue space w/ macrophages
- Basal lamina of ERCs
- ERCs
Why is the medulla paler than the cortex?
the cortex has many more premature t lymphocytes
The left picture is taken in the ____.
The light cells are ___
The darker cells are ___.
It’s in the medulla because that’s a Hassal’s corpuscle.
The light cells are ERCs (prob type 5)
The darker cells are T lymphocytes
What is the green arrow pointing to?
What is the blue arrow pointing to (darker cells)?
Green = type 2 ERC
Blue = t lymphocyte
MOST lymphocytes from bone marrow follow what pathway in lymph nodes?
- T & B cells enter through the artery at the hilum
- Exit the blood vascular system via high endothelial venules in the deep cortex
- Parenchyma of the deep cortex to find their specific antigen
- Lymphatic sinusoids
- Exit via efferent lymphatic vessel
- Return to blood vascular system via lymphatic vascular system
Distinguishing features of thymus
Lacks lymphatic nodules
Affterent lymphatic vessels
Hassall’s corpuscles
Functions of lymph nodes
filter lymph
lymphocyte proliferation
antibdoy production
recirculation of lymphocytes
Lymph nodes are located strategically along the passageways of lymphatic vessels.
STructure of a lymph node
- Kidney-shaped w/ a hilum
- Capsule & septa w/ sinuses
-
Parenchyma:
- Cortex: B cells, lymphoid nodules
- Paracortex/Deep cortex: T cells, high endothelial venules (HEVs)
- Medulla: Plasma cells, medullary cords
- Stroma: reticular cells & reticular fibers
- Both afferent & efferent lymphatic vessels
High endothelial venules are what kind of endothelial cells
simple cuboidal
Pathway of humoral immunity
- Pathogen enters afferent lymphatic vessel (1) and gets recognized by B cells in the outer cortex and T cells in the deep/inner cortex.
- T cells proliferate to make more Th cells
-
Th cells go to the lymphatic follicle to cause the activated B cells proliferate and become centroblasts (B cells that are ready to become plasma cells)
- Centroblasts are paler (that’s why the germinal center is pale) because their nucleus is euchromatin
- Plasma cells go to the medulla, make antibodies, and eventually enters the efferent lymphatic vessels.
How is lymph circulated?
- Enters via afferent lymphatic vessel into the subscapular sinuses (has macrophages here)
- Macrophages here will phagocytose, but also present antigens for the T helper cells in the paracortex
- Follow paratrabecular sinuses
- Medullary sinuses
- EFferent lymphatic vessels
This is a lymph node. What are the blue arrows pointing at?
Subscapular sinus: where afferent lymphatic vessels enter; many macrophages here
The bottom most arrow points to
Paratrabecular sinus: where the lymph will be transported deep tothe cortex
The blue circle contains
Germinal center: contains activated B cells/centroblasts
90% of lymphocytes enter a lymph node via
HEVs in the paracortex.
(simple cuboidal, unlike capillaries)
Primary vs secondary follicles of the cortex
Primary follicles don’t have a germinal center yet.
Secondary follicles do
Paracortex lacks nodules and has what kind of cell?
T cells
What region of the lymph node is this slide taken from?
Circles are plasma cells (clockface nucleus). The arrows are lymphocytes (dark). This is the medullary region.
Structure of the spleen
- Triangular shaped w hilum
- Connective tissue capsule & septa
-
Parenchyma:
- White pulp: Central arteriole, PALS, corona, germinal center
- Red pulp: splenic cords, splenic sinusoids
- Stroma: reticular fibers & cells
The blue arrow points at
white pulp
Where do you see B cells and T cells in the spleen?
B cells in the germinal centers
T cells in the PALS
note: they’re always close by each other
Function of the white pulp
- Lymphocyte proliferation (T & B cells)
- APC’s
- Antibody production
- Remove blood antigens
Pathogens enter the spleen through
the blood - the central arteriole
Function of red pupl
- Remove blood antigens
- Aged, abnormal damaged RBCs & platelets leaving the capillary can’t squeeze into the sinusoid, so they get eaten by macrophages.
- Retrieval of iron (macrophage phagocytosis & digestion)
What are the reddish lines the blue arrow is pointing at in this pic of a spleen?
What are the white areas?
Reticular fibers.
Sinusoids.
what is this
tonsil
what is this
peyer’s patches of the ileum
Peyers patches
