Immune-Thymus Flashcards
describe the general organization of the immune system
a one-way system with blind collection conduits that connect to pipes that prevent backflow and lead to a series of treatment centers where liquid and chemicals input (conduits and pipes are lymphatic vessels and treatment centers are lymphatic organs and tissues)
what are the 2 types of cells in the immune system?
- migratory cells (lymphocytes)
- fixed cells (mesenchymal or epithelial cells
describe the migratory cells/lymphocytes of the immune system (2)
- free to move anywhere in body
- ensure effective surveillance of ALL tissues
describe the fixed cells/mesenchymal or epithelial cells of the immune system
- restricted to a lymphatic organ, forming its stroma
- create a microenvironment that is supportive of leukocyte development
what are the 2 types of migratory cells/lymphocytes?
- T cells
- B cells
what type of immunity do B cells contribute to? where are they found?
humoral immunity, concentrated in lymphoid organs
what are B cells precursors to? what is the function of what they become?
precursors to plasma cells; plasma cells produce immunoglobulins (antibodies)
what type of immunity do T cells contribute to? where are they found?
cell-mediated immunity; concentrated in lymphoid organs and also circulate through peripheral blood and body tissues
what is the function of T cells upon stimulation?
upon stimulation they proliferate and secrete cytokines (lymphokines)
what is the function of primary lymphoid tissue?
produce lymphocytes committed to either B cell or T cell lineage
does development and differentiation of lymphocytes within primary lymphoid tissue occur via use of foreign antigen? what does this mean for the lymphocytes that are developed?
no! occurs independent of foreign antigen so the cells developed and differentiated in primary lymphoid tissue are naive or virgin cells ;)
what are 3 examples of primary lymphoid tissue?
- bone marrow
- gut-associated lymphoid tissue (ileal peyer’s patch)
- thymus
describe bone marrow as a primary lymphoid tissue (2)
- origin of B and T cell precursors
- major site of hematopoietic cells
describe gut-associated lymphoid tissue (ileal peyer’s patch) as a primary lymphoid tissue
lymphoid nodules in distal jejunum/ileum in young ruminants, pigs, and carnivores
describe the thymus as a primary lymphoid tissue (2)
- site of development of all cell-mediated immunity
- where naive lymphocytes turn into mature T lymphocytes!!
describe secondary lymphoid tissues (2)
- specialized microenvironments located throughout the body that expose lymphocytes to foreign antigen
- strategically located in sites of the body of entry of foreign antigens
give 3 examples of secondary lymphoid tissue
- lymph nodes
- spleen
- mucosa-associated lymphatic tissue (MALTs)
what is indicated if all lymph nodes are enlarged?
systemic infection or lymphoma
what is the function of the spleen?
like a lymph node for the blood, monitors blood for foreign antigen to expose lymphocytes to
what are 3 MALTs?
- tonsils
- gut-associated lymphatic tissue (GALTs)
- bronchus-associated lymphoid tissue in the lungs
what are the 2 parts of an immune organ? describe what is found in each
- stroma: fixed cells
- parenchyma: lymphocytes and antigen presenting cells
what are the fixed cells of the stroma of an immune organ? describe (3)
reticular cells
1. fibroblastic origin
2. synthesize reticular fibers
3. have a stellate or fusiform appearance
what are the capsule and septae of the thymus composed of? how is it organized?
loose CT that divides into lobes that then divide into lobules
describe the cortex of the thymus (2)
- peripheral region of each lobule
- contains a thymic/blood barrier
what is the function of the thymic/blood barrier in the cortex of the thymus?
alters vasculature to protect growing/maturing T cells
describe the medulla of the thymus (2)
- central region of each lobule
- NO thymic/blood barrier
what is the corticomedullary junction of the thymus?
the central region between the cortex and medulla; the region where lymphocytes enter the thymus from the bone marrow
what is the function of the thymus?
a site of development of all cell-mediated immunity (where naive T lymphocytes differentiate into mature T lymphocytes
describe the thymus as a lymphoepithelial organ
epithelial cells encompass T cells and help develop a unique environment between epithelial cells and differentiating thymocytes that are still developing in the thymus
what do fibroblasts come from?
mesenchyme!
what are the main cells of the thymus? describe (3)
thymic epithelial cells (TECs)
1. ovoid pale-staining nuclei
2. form an interconnecting meshwork of processes
3. believed to produce thymopoietin (a thymic hormone) and additional factors that influence the differentiation of T-lymphocytes
describe the capillaries of the cortex and medulla of the thymus
cortex: continuous; don’t leak so that can maintain thymic/blood barrier
medulla: fenestrated (leaky) capillaries because no thymic/blood barrier
describe the journey of T cells through the thymus
- begin as hematopoietic precursors from the bone marrow and migrate to the thymus, where they are now called thymocytes
- in thymus, undergo positive selection to ensure they react to foreign antigen and negative selection to make sure they do not react to self-antigen
describe positive selection of T cells; where does it occur?
positive selection in the thymus selects cells with a T cell receptor that is able to bind to MHC I or II with at least a weak affinity, eliminating the non-functional cells; occurs in the cortex of the thymus
describe negative selection of T cells; where does it occur?
active induction of apoptosis in thymocytes with a high affinity for self peptides or MHC; if attack body’s own proteins, cell is eliminated in the thymus; occurs in the cortex/medulla of thymus
what does a mature T cell epxress?
either CD4 or CD8; but not both!
