Lecture 7: The lymphoreticular system I Flashcards
What is the immune system?
A network of soluble proteins, cells, tissue and organs that defend the body against ‘foreign invaders’
What are white blood cells called?
Leucocytes
What are the two broad groups of leucocytes?
Lymphoid cells and phagocytes
What are lymphoid cells?
Lymphocytes and plasma cells
What are the different types of phagocytes?
Granulocytes and mononuclear phagocytic system
What are the different types of granulocytes?
Neutrophils, eosinophils and basophils
What cells make up the mononuclear phagocytic system (MPS)?
Monocytes, macrophages and dendritic cells
What is the lymphoreticular system?
Complex organisation of cells of the lymphoid and mononuclear phagotic system components of the immune system
What were cells of the MPS previously known as?
Reticuloendothelial cells
Why were cells of the MPS previously known as reticuloendothelial cells?
Their tendency to form a network (reticulum) by cytoplasmic extensions
Where are cells of the lymphoreticular system found within the body?
Distributed in various organs/tissues
What do lymphoreticular cells do?
Coordinate immune response
What is the name given to the process of blood cell formation?
Haematopoiesis
What is the name of the stem cell that gives rise to the all leucocyte cells?
Multipotential hematopoletic stem cell (hemocytoblast)
The myeloblast cell differentiates to give rise to which cells?
Granulocytes (basophil, neutrophil, eosinophil) and monocytes
Monocytes give rise to which types of cell?
The macrophage and dendritic cell (mononuclear phagotic system cells)
T lymphocyte and B lymphocyte arise from the differentiation of which cell type?
Small lymphocyte
Plasma cells arise from what type of cell?
B lymphocyte
Hemocytoblast differentiates into what two cell types?
Common myeloid progenitor and the common lymphoid progenitor
What is bone marrow?
The site of haematopoiesis and occupies medullary cavity of bones
Where is bone marrow found in adult bodies?
Limited to the axial skeleton
What three cell types make up bone marrow?
Hematopoetic cells
Adipocytes (lipocytes)
Megakaryocytes
What do lymphocytes do?
Play a key role in the immune system providing a learned/targeted (adaptive) response
How much of the WBC circulation do lymphocytes make up?
20-50%
When do the number of lymphocytes increase?
With viral infection
How large are small lymphocytes?
6-9 nanometers
What is the appearance of the lymphocytes nucleus?
Round/oviud nucleus, dense chromatin, nucleoli not usually visible
What is the appearance of a lymphocytes cytoplasm?
Thin rim of basophilic cytoplasm
Where are T lymphocytes found within the body?
Immature T cells originate in bone marrow but migrate to mature in the thymus
What are the functions of T cells?
Effector and regulatory functions
What do t lymphocytes develop into?
Different functional sub sets: t helper cells, cytotoxic t cells and regulatory t cells
What do T helper cells do?
Help other immune cells (B cells, cytotoxic T cells and antigen presenting cells)
What do cytotoxic t cells do?
Kill virus infected cells and cancer cells
What do regulatory t cells do?
Suppress immune responses
What antigen do cytotoxic t cells have?
CD8
What antigen do helper t cells have?
CD4
Where do B lymphocytes mature?
Bone marrow
How are B cells activated?
B cell receptor (BCR) binds antigen (with the help of a T-helper cell)
What happens once a B cell is activated?
Undergoes mitosis, stimulated cells mature into plasma cells or memory B cells
What do plasma cells produce?
Large amounts of immunoglobulin (antibody)
What are monocytes?
Highly phagotic cells (ingesting microorganisms, cell devris and particulate matter)
Where do monocytes mature?
In tissues, into macrophages
How large are monocytes?
Up to 20 micrometers diameter (largest of WBC)
How much of the WBC circulation is made up of monocytes?
2-10%
Describe the nucleus of a monocyte
Large, eccentrically placed
Stains less intensely dye to more open chromatin)
Kidney bean shape or folded usually
What is the appearance of a monocytes cytoplasm?
Abundant and pale
What are macrophages?
Large phagocytic immune cells found in tissues that have differentiated from monocytes
What are tissue macrophages?
Populations of macrophages through the body that perform immune surveillance activities
What are some immune serveillance activities?
Phagocytosis, antigen presentation and immune suppression
What are dendritic cells?
Cells which process antigenic material and present it on the cell surface to a T cell
Where are dendritic cells found?
Tissues in contact with the external environment such as the skin (Langerhans cells)
What is the innate immune system?
System which provides a rapid immune response to infectious agents/toxins
What are the cellular components of the innate immune system?
Granulocytes and mononyclear phagotic system (MPS)
What are the protein/peptide components of the innate immune system?
Complement, acute-phase proteins, chemokines and interleukins
What does the innate immune response result in?
Inflammation
What do the cells and proteins of the innate immune system support?
The adaptive immune system
What characterises the adaptive immune system?
The ability to learn and memory
What does it mean that the adaptive immune system has the ability to learn?
Subsequent encounters with a pathogen elicit faster, specific and greater responses
Why does adaptive immunity rely of cell division (mitosis)?
To produce large numbers of lymphocytes with specificity towards a pathogen or antigen
How long does it take for the adaptive immune system to develop a significant response?
3-5 days
How do lymphocytes in the adaptive immune system attack pathogens?
Cellular response (T cells) or humoral response (B cells) or a combination
How is adaptive immune system influenced by the innate response?
It is controlled by and amplifies the innate response
What is the diversity of the innate immune system?
Limited; germline encoded
What is the diversity of the adaptive immune system?
Large, receptors are produced by somatic recombination of gene segments
What cells make up the adaptive immune system?
Lymphocytes
What cells make up the innate immune system?
Phagocytes (macrophages, neutrophils,) natural killer cells, innate lymphoid cells
What are antigen presenting cells?
Heterogenous group of immune cells that mediate cellular immune responses by processing and presenting antigens fro recognition by T cells
What are some classical antigen presenting cells?
Macrophages, B cells, DCs
Explain T cell-independent B cell activation
Antigen on bacterium binds to B cell receptor, activated B cell undergoes clonal selection, cell proliferates, clonal expansion?
What is the thymus?
Flattened lymphoid organ located in the anterior mediastinum/base of neck
When is the thymus most active?
During childhood/puberty, then slowly involutes
Why does the thymus secrete hormones?
To regulated T cell maturation, proliferation and function
What does the thymus develop immunocompetent T cells from?
Bone marrow derived precursors
Why does the thymus proliferate clones of mature naive T cells?
To supply the circulating and peripheral tissues
Explain how the thymus functions in immunological self-tolerance?
Apoptosis of self-reactive T cells
What does the thymus originate from?
Epithelial outgrowths which merge to form a single organ subdivides into fine lobules
How does the epithelium of the thymus develop?
Into a sponge like structure with interconnecting spaces
What are the spaces in the thymus colonised by?
Immature and maturing T lymphocytes
What do epithelial cells in the thymus provide for lymphocytes?
Mechanical supporting framework
What happens towards the centre of each lobule of the thymus?
Epithelial framework forms a coarser structure with smaller spaces
What are the two regions of the thymus’ lobules?
Outer cortex (more cellular) Inner medulla (less cellular)
How do lymphocytes move in and out of the thymus?
Post capillary venules in the corticomedullary region have specialised endothelial cells
In adults, lymphoid tissue is separated by?
Adipose tissue
Where do immature T cells enter the thymus?
Cortico-medullary junction
What name is given to the region where immature T cells undergo maturation after entering the thymus?
Thymic cortex
What happens in the outer cortex of the thymus?
Lymphoblasts divide by mitosis to produce clones of smaller mature T cells
What happens to T cells as they move towards the medulla?
Further maturation
What cells in the outercortex promote T cell maturation?
Thymic nurse (epithelial) cells
What cells take up apoptotic cells in the thymus
Macrophages
The epithelial framework of the thymic cortex is?
Finely branched (not see on H&E stain)
Maturing T cells migrate from the thymic cortex to the …
thymic medulla
What is the appearance of the thymic medulla compared to the cortex?
Epithelial component is more apparent, large pale-stained nuclei and eosiniphilic cytoplasm
What name is given to the groups of keratinised cells in the medulla of the thymus
Hassal corpuscles
What are thymic interdigitating cells?
Dendritic cells found in the medulla
What do dendritic cells in the thymic medulla do
Play a role in clonal deletion (negative selection) of self-reactive T cells
What do mature T cells do from the thymic medulla?
Enter blood and lymphatic vessels
