Ch. 2 Cells of the Immune System Flashcards
What type of stem cell differentiates into all the blood cells needed by the body?
Hematopoietic stem cells
Multipotent
multiple+ able; develop into multiple types of cells
Hematopoiesis
blood+making
what are the two types of common progenitor cells?
- Common myeloid progenitor
- common lymphoid progenitor
What types of cells stem from the common myeloid progenitor cells?
- RBCs, platelets, granulocytes, monocytes, macrophages, dendritic cells
- makes the most different types of cells
What types of cells stem from the common lymphoid progenitor cells?
gives rise to all B cells, T cells, NK cells, dendritic cells
What are the three primary ways blood cells are distinguished?
- appearance and behavior
- flow cytometry
- fluorescence microscopy
Neutrophils
- most common
- nuclei stain deep purple
- granules/cytoplasm stain lilac
- highly motile and extremely phagocytic
During infection, numbers of ______ increase significantly and are recruited to the site of infection by damage cues (chemokines).
neutrophils
Eosinophils
- minority (1-4%)
- nuclei stain deep purple
- granule contents are basic, making them attractive to eosin staining them more pink
- motile and phagocytic
- significant role in response to large, multicellular pathogens like parasitic worms
Basophils
- very small minority
- nonphagocytic and contain large cytoplasmic granules filled with acidic contents
- stain very well with basic hematoxylin (deep purple)
- in response to infection, they release their granules, which are filled with histamine
Mast cells
- undifferentiated cells
- released from the bone marrow as undifferentiated cells
- only mature after leaving the blood and taking up residence in tissues
- full of histamine
- responsible for allergies; inflammation
- phagocytose
Where are mast cells located?
in skin, CT, and mucosal epithelia in respiratory, genitourinary, and digestive tracts
Why is leukocytosis a sign of infection?
It is an increase in circulating neutrophils, which will only increase if there is infection.
What is the primary cell type found in pus?
neutrophils
What are NETs?
self sacrifice and project strands of their own DNA to ensnare pathogens
What is NETosis?
form of cell death (apoptosis of neutrophils)
What effects does histamine release have on the body?
histamine induces inflammation
What granulocyte is primarily responsible for allergies?
mast cells
What is the purpose of antigen-presenting cells?
a group of cells that function as cellular bridges between innate and adaptive immune systems
During antigen presentation, if a T cell is presented its _____ _____, it will activate and begin adaptive immune responses.
cognate antigen
Monocytes
o Make up 4-8% of leukocytes (WBC)
o Circulate in blood, but can migrate into tissues in response to infection signals
o In tissues, can further differentiate into macrophages or dendritic cells
o Large nuclei compared to other, agranulocyte
Macrophages
o Pathogens marked with soluble antibody are said to be opsonized (make tasty)
o Can very efficiently engulf opsonized pathogens
o This means that once adaptive immunity is fully activated and B cells are making antibody against a pathogen, macrophages are crazy effective and finding and destroying
o (a monocyte that has navigated to tissue)
Dendritic Cells
o Critical initiators of immune responses as a key bridge between innate and adaptive immunity
o Capture antigen just like other APCs, but their long dendritic extensions make their surface area large
Can interact with many T cells at once, making them super activators of the adaptive immune response
AKA: THE most important APCs
are the most potent APC for activating naïve T cells
• Take in antigen by phagocytosis, endocytosis, and pinocytosis
What cell type is responsible for forming platelets that are a necessary aspect of blood clot formation?
megakaryocytes
What cells are part of the lymphoid lineage?
B lymphocytes
T lymphocytes
NK cells
Where do B cells develop?
bone marrow
What do activated B cells do?
- Act as APC (phagocytic and can present to T cells)
- Express costimulatory receptors to activate T cells
- Develop into plasma cell
Where do T cells develop?
thymus
Is an NK cell an adaptive lymphocyte or an innate lymphocyte?
innate lymphocyte
How does an NK cell decide which cells too kill?
attacks abnormal cells that lack MHC expression
Where does the majority of hematopoiesis occur in a developing fetus during the first trimester?
yolk sac
Where does the majority of hematopoiesis occur in a developing fetus during the second trimester?
liver
Where does the majority of hematopoiesis occur in a developing fetus during the third trimester?
bone marrow
As humans age, we lose some of the areas where hematopoiesis occurs. Compare the areas that serve as hematopoiesis zones in a 10 year old, 25 year old, and a 50 year old.
10: vertebral and pelvis, tibial, sternum, ribs
25: vertebral and pelvis, sternum, ribs
50: vertebral and pelvis, sternum, ribs
What type of cells are present in the bone microenvironment?
HSCs reside in specialized microenvironments, or stem cell niches. Lined with supportive cells that regulate survival, proliferation, differentiation, and trafficking.
• Osteoblasts generate bone and control HSC differentiation
• Endothelial cells line blood vessels and regulate HSC differentiation
• Sympathetic neurons control release of cells from bone marrow
• HSCs and progenitor development are controlled with a stream of cytokines and growth factors
Why does bone get less and less able to perform hematopoiesis as we age?
as we age, bone marrow is slowly converted to adipose tissue; approaches 50% and decreases hematopoiesis
Where do T cells develop?
T cell progenitors develop initially in the bone marrow, but then migrate to the thymus where they achieve full maturity.
What is negative selection of T cells?
if bind too tightly or recognize self-peptides (Kills every cell that recognizes self-molecules and will not attack body)
What is positive selection of T cells?
if bind “just right” ensuring they will recognize MHC. (Kills every cell that doesn’t match MHC)
What are the three primary secondary lymphoid organs?
- lymph nodes
- spleen
- X-associated lymphoid tissue
What do all secondary lymphoid organs have, despite their different overall anatomies?
- anatomically distinct regions of T cell and B cell activity
- lymphoid follicles
How are SLOs connected?
via the blood and lymphatic circulatory systems
How much lymph fluid is returned to the circulatory system each day?
~2.9 L a day
What can occur when lymph is not efficiently returned to the circulatory system?
lymphedema results and effects on immune reaction are evident
Where do T cells enter a lymph node?
o Naïve T lymphocytes enter via the high endothelial venules of the blood stream to enter the cortex.
Where do B cells enter a lymph node?
through high endothelial venules (like T cells)
Where are T cells found when they are searching for antigen?
o They browse APCs in the paracortex (takes 16-24 hours to browse the APCs in a single lymph node)
APCs on a network of fibers created by fibroblastic reticular cells known as the fibroblastic reticular cell conduit system.
• This system serves as a highway where T cells are guided by adhesion molecules and chemokines
Where do nonactivated lymphocytes exit?
o If they do not find their MHC peptide match, they leave via the efferent lymphatics (T cells)
Effector memory cells
continue to circulate among all tissues
Central memory cells
take up residence in secondary lymphoid organs
Resident memory cells
settle in nonlymphoid tissue
What occurs in germinal centers?
facilitate the generation of B cells with increased receptor affinity through somatic hypermutation
What dictates which B cells live to become effector plasma cells?
- activated b cells fight for antigen in these centers
- once done, the surviving cells make even better antibodies and move to the medulla to secrete antibodies into the bloodstream
- germinal centers take 4-7 days to establish and last about 3 weeks
Where do antigens/APCs enter the spleen?
via splenic artery
Where are T cells found when they are searching for antigens in the spleen?
browse APCs in PALS
Where are B cells found when they are searching for antigens in the spleen?
encounter antigen in follicles, find TH match, and then create germinal centers in follicles
Where do nonactivated lymphocytes exit the spleen?
splenic artery
What does NET stand for?
Neutrophil Extracellular Trap
How do CD4+ cells recognize antigens?
- professional APCs use MHC II to present
- browse surfaces of APCs with TCRs looking for matching antigen (if found become subset of T cells)
How do CD8+ cells recognize antigens?
-somatic cells use MHC I to present
-browse surfaces of APCs with TCRs looking for match
-if found, activate and become effector cytotoxic T cells
(great for virus-infected cells, tumor cells)
Once activated, Helper T cells produce cytokines to activate:
B cells, Cytotoxic T cells, macrophages, etc.
-changes behavior and response of immune system
Antigen Presenting Cells include:
- monocytes
- macrophages
- dendritic cells
Cluster of Differentiation
defined subset of cellular surface receptors that ID cell type and stage of differentiation, and which are recognized by antibodies
What is the difference between the activation of NK cells and CD8+ cells?
- CD8+ cells browse APCs for antigen to match their antigen receptors
- NK cells attack cells that do not display MHC I receptors. Do NOT have antigen-specific receptors
Function of Osteoblasts
generate bone and control HSC differentiation
Function of Endothelial cells
line blood vessels and regulate HSC differentiation
Function of sympathetic neurons
control release of cells from bone marrow
Where does entry of naive double negative thymocytes occur?
CMJ
Where do double negative thymocytes proliferate and generate TCRs, CD4, and CD8?
subscapular cortex
Where are double positive thymocytes tested for their ability to bind MHC complexes via cTECs? (Positive selection)
cortex
Double positive thymocytes are tested for their ability to bind MHC cocmplexes via
cTECs
Single positive thymoctyes are tested for their ability to bind proteins found in other organ types via mTECs in the
medulla
Single positive thymocytes are tested for their ability to bind proteins found in other organ types via
mTECs
Lymphoid follicles
organized microenvironments that are responsible for the development and selection of B cells that produce high-affinity antibodies
In a lymph node, where are B cells located?
cortex
In a lymph node, where are T cells located?
paracortex
In a lymph node, where do lymphocytes exit and plasma cells make antibodies to enter circulation?
medulla
