What are the different types of haematopoeisis that take place to generate the body's immune system?
Erythropoesis - red blood cells aka erythrocytes
Myelopoeisis - granulocytes (neutrophils, basophils, eosinophils) & monocytes (macrophages)
Lymphopoeisis - lymphocytes ie., T-cells & B cells
Thrombopoeisis - platelets
What is meant by "microenvironment" of stem cells that give rise to blood cells? What, besides stem cells, are necessary in those microenvironements for successful haematopoesis
The microenvironment refers to both location of haematopoesis and blood-cell-specific soluble factors involved in regulatory signalling.
Eg. Erythopoeisis's microenvironment involves the bone marrow, where stem cells are exposed to soluble factors made in the bone marrow (SCF - stem-cell factor), in the bone itself (IL-6 - interleukin 6) and in the kidney (EPO-erythropoeitin).
Without these soluble factors, stem cells would not differentiate into erythrocytes.
What role do the foetal liver, spleen & kidney play in erythropoeis?
Erythropoeisis begins early in development in foetal liver & spleen, then moves into the bone marrow of the foetus.
Eventually, in adulthood, eryrthropoeisis takes place in the red & yellow marrow of the adult's long bones (femur & humerus). The flat bones -- skull, sacrum, pelvis -- and vertebrae remain active sites of erythropoeisis in adulthood, but mostly red marrow. The liver and spleen also remain active; the spleen's red matter acts as a reservoir of RBCs.
Low oxygen tension in the kidney's proximal tubule stimulates Epo production; EPO is a soluble factor that induces globin synthesis at the early stages of stem-cell differentiation.
What are the stages of stem-cell development into erythrocytes?
1. Stem cells
2. Erythroid ala Colony-Forming Unit (CFU) - stimulated by EPO produced in PCT of kidney under low O2 tension
3. Rubiblast (Rb)
4. Prorubicyte (Pr)
5. Rubicyte (Rt) - basophilic, then polychromatophilic
6. Erythrocyte - red blood cell
What happens to the nucleii of differentiating erythroblasts (eg., rubiblasts, prorubicytes, rubicytes) in the bone marrow, and how to the anucleated erythrocytes leave the bone marrow?
In the bone marrow, differentiating erythroblasts surround a centrally located macrophage, which digests the discarded nuclei of the erythroblasts.
Once they reach erythocyte stage, they exit bone marrow via sinusoidal capillaries into bloodstream, where they proceed to the spleen, liver and other tissue at high O2 carrying capacity.
What is the life span of erythrocytes in dogs & cats?
Dogs - 100 days
Cats - 70 days
(Humans - 120 days)
What is the function of erythrocytes?
Carry O2 to tissues and CO2 away from tissues.
What is the function of platelets?
What are the stages of development of thrombocytes, and what are the soluble factors necessary for their development?
Platelets, or thrombocytes, are fragments derived from cytoplasm of precursor megakaryocytes in bone marrow, so they don't go through developmental stages in the same was as erythroblasts become erythrocytes.
Platelets "bud off" from the nucleated megakaryocytes and enter the blood via sinuses from the bone marrow.
Thrombopoeitin (TPO) is the soluble factor related to platelets. TPO is made in the liver.
What is the name of stem cells in bone marrow that will become either granulocytes or monocytes?
What are the stages of development & proliferation of neutrophils from myeloid cells in the bone marrow to circulating in blood.
.1. Pluripotent stem cell
2. Proliferation Neutrophil Pool: a mitotic pool, stimulated by IL-1, IL-3, IL-6, GM- CSF & G-CSF; lasts about three days; apoptosis occurs here to limit production of myelocytes
b. Progranulocyte (Pg)
3. Maturation Neutrophil Pool: post-mitotic pool, lasts 2-3 days in dogs
b. Band neutrophil
c. Segmented neutrophil
4. Storage Neutrophil Pool: Subpool of Mature Neutrophil Pool containing band neutrophils and segmented neutrophils, ready to be released to marrow sinusoids into blood, and then to migrate to tissues
5. Circulating Neutrophil Pool
6. Marginated Neutrophil Pool - the neutrophils that are ready to exit circulation and migrate into:
7. Tissue Neutrophil Pool - neutrophils ADHERE to tissues via adhesion molecules in endothelial cells
What are the different cytokines/soluble factors involved in myelopoesis & what do they do?
Cytokines secreted by stromal cells (macrophages, fibroblasts, endothelial cells):
Interleukin-1 (IL-6) - stimulates granulocytic cells
Interleukin-3 (IL-3) - stimulates growth in ALL phagocytes (granulocytes & monocytes)
Interleukin-6 (IL-6) - stimulates multiple cell types to proliferate
Cytokines secreted macrophages, T-cells, mast cells, NK cells, endothelial cells & fibroblasts; provide positive feedback loop for monocyte; stimulate stem cells to produce granulocytes & monocytes:
GM-CSF - granulocyte- macrophage colony stimulating factor
G-CSF - G-CSF - granulocyte colony stimulating factor
T-cells, B- cells and eyrthrocytes are all about the same size. How are they distinguished from each other.
RBCs don't have nucleii, except avian RBCs.
T-cells and B-cells have large round nucleii that occupy most of their cytoplasm, but they look identical under light microscope. They must be identified by their receptors, using immunohistochemistry or flow cytometry.
What are the roles of the bone's extracellular matrix and stromal cells in haematopoeisis?
In the bone marrow, the fibroblasts and osteoblasts of the extracellular matrix secrete fibronectin, laminin and collagen to serve as adhesion cells, as well as soluble factors, while the stromal cells in the bone such as macrophages, fibroblasts and endothelial cells in the marrow also produce soluble factors such as stem-cell factor (SCF), IL-1, IL-3, IL-6, GM- CSF & C-CSF.
Epo is produced in the kidneys.
What is the name given to the development of macrophages in the bone marrow?
What are the stages of monopoeisis and what are the soluble factors that affect the development of monocytes & macrophages?
First, note that monocytes and macrophages are the same thing. Monocytes circulate in blood & macrophages are found in tissue.
1. Pluripotent stem cell
2. Myeloid cell
5. Monocyte / Macrophage
Cytokines involved are:
IL-3, IL-6 & GM-CSF, M-CSF
Monocytes, macrophages & granulocytes all engage in phagocytosis. What are the names of the phagocytic cells found in tissue throughought the body, starting from the brain?
Brain: microglial cells
Lung: alveoloar macrophages
Liver: Kuppfer cells
Kidney: mesangial cells
Blood: monocytes, neutrophils
Lymph node: resident & circulating macrophages
Bone: precursors in bone marrow (monoblasts, progranulocytes)
Joints: synovial A cells
Test Dog 1 Reference Range
WBC (total) 9.48 6 -17.1 x109/l
Neutrophils 8.4 3 – 11.5 x109/l
Lymphocytes 0.2 1 – 4.8 x109/l
Monocytes 0.48 0.15 - 1.5 x109/l
Eosinophils 0.4 0 - 1.3 x109/l
Basophils 0.0 0 - 0.1 x109/l
Interpret & explain the haematological abnormality or abnormalities in Dog 1.
• All parameters are within normal limits with the exception of the lymphocyte count, which is below the reference range
• Lymphopenia is commonly seen in acute viral infection as the lymphocytes leave the circulation and enter secondary lymphoid tissues to look for antigen, or into infected tissues looking for the pathogen
Test Dog 2 Reference Range
WBC (total) 32.8 6 -17.1 x109/l
Neutrophils * 26.1† 3 – 11.5 x109/l
Lymphocytes 3.6 1 – 4.8 x109/l
Monocytes 2.3 0.15 - 1.5 x109/l
Eosinophils 0.8 0 - 1.3 x109/l
Basophils 0.0 0 - 0.1 x109/l
* band neutrophils found
Interpret & explain the haematological abnormality or abnormalities in Dog 2.
• High WBC count, predominantly made up of neutrophilia, with left shift (band neutrophils) and monocytosis (high level of monocytes)
• This is consistent with a bacterial infection as cytokines are released during inflammation (e.g. GM-CSF) that stimulate bone marrow production of these myeloid cell types.
• Neutrophils and monocytes travel to the sites of infection where the monocytes differentiate into tissue macrophages. Both cell types subsequently phagocytose bacteria and stimulate an inflammatory reaction in infected tissues.