C5 - LESSON 1: LYMPHOID ORGANS Flashcards
Largest tissue of the body (adult: 1300 to 1500g)
Bone Marrow
Main source of hematopoietic stem cells
Bone Marrow
Can differentiate into lymphocytes and other hematopoietic cells such as granulocytes, erythrocytes, and megakaryocyte population.
Bone Marrow
Center for antigen independent lymphopoiesis
Bone Marrow
B cell maturation takes place within the bone marrow itself
Bone Marrow
Small, flat, bilobed organ found in the thorax or chest cavity, right below the thyroid gland and overlying the heart.
Thymus
Weighs an average of 30g at birth, reaches about 35 g at puberty, and then gradually atrophies
Thymus
Although the thymus diminishes in size, it is still capable of producing T lymphocytes until at least the fifth or sixth decade of life.
Thymus
Progenitor cells that migrate to the thymus proliferate and differentiate under the influence of the humoral factor-(?)
thymosin
- lymphocyte precursors with acquired surface membrane antigens
Thymocytes
Surface antigens are acquired as the lymphocytes travel from the cortex to the medulla over a period of 2 to 3 weeks.
Thymus
Progenitors of T cells appear in the fetus as early as 8 weeks in the gestational period - essential to acquisition of immunocompetence by the time the infant is born.
Thymus
Secondary Lymphoid Organs
act as lymphoid filters in the lymphatic system
Lymph nodes
Lymph fluid flows slowly through spaces called (?), which are lined with macrophages, creating an ideal location for phagocytosis to take place.
sinuses
respond to antigens introduced distally and routed to them by afferent lymphatics
Lymph nodes
Generalized lymph node reactivity can occur after (?) (e.g., serum sickness)
systemic antigen challenge
Lymph nodes Primary function:
generation of B cell memory
The Lymph nodes tissue is organized into:
Contains macrophages and aggregations of B cells in primary follicles
Outer cortex
These are mature, resting B cells that have not been exposed to antigens.
Outer cortex
Specialized cells called follicular dendritic cells are also located here
Outer cortex
Region between the follicles and medulla where T lymphocytes are mainly localized
Paracortex
T lymphocytes are in close proximity to antigen-presenting cells called interdigitating cells
Paracortex
Particulate antigens are removed as the fluid travels across the node from cortex to medulla.
Inner medulla
The transit time through a lymph node is approximately 18 hours.
Inner medulla
If contact with antigen takes place, lymphocyte traffic shuts down due to the proliferation of activated cells.
Inner medulla
Accumulation of lymphocytes and other cells causes the lymph nodes to become enlarged, a condition known as lymphadenopathy.
Inner medulla
Recirculation of expanded numbers of lymphocytes then occurs.
Inner medulla
Largest secondary lymphoid organ
Spleen
It is an important site of antibody production in response to IV particulate antigens (e.g., bacteria)
Spleen
acts as a lymphatic filter within the blood vascular tree
Spleen
Two main types of splenic tissue:
removes old and damaged cells and foreign antigens from the blood.
Spleen
Makes up more than one-half of the total volume
Red pulp
Red pulp Function:
to destroy old red blood cells
20% of the total weight of the spleen
White pulp
Contains lymphoid tissue- arranged around arterioles in a periarteriolar lymphoid sheath (PALS)
White pulp
- contains mainly T cells
PALS
- attached to the sheath
Primary follicles
contains B cells that are not yet stimulated by antigens
Primary follicles
- surrounds the PALS containing dendritic cells that trap antigen
Marginal zone
includes lymphoid tissue in the intestines (Peyer’s patches) and the liver
GALT (Gut-associated lymphoid tissue)
features immunoglobulin A (IgA) production and involves a unique pattern of lymphocyte recirculation.
GALT (Gut-associated lymphoid tissue)
important for the development of tolerance to ingested antigen
GALT (Gut-associated lymphoid tissue)
Rich source of mature T cells
Thoracic duct
can cause T cell depletion and has been used as a method of immunosuppression.
Chronic thoracic duct drainage
includes lymphoid tissue in the lower respiratory tract and hilar lymph nodes.
BALT (Bronchus- associated lymphoid tissue)
It is mainly associated with IgA production in response to inhaled antigens.
BALT (Bronchus- associated lymphoid tissue)
Antigens introduced through the skin are presented by epidermal Langerhans cells, which are bone marrow–derived accessory cells.
Skin-associated lymphoid tissue/ Cutaneous-associated lymphoid tissue
These epidermal cells then interact with lymphocytes in the skin and in draining lymph nodes.
Skin-associated lymphoid tissue/ Cutaneous-associated lymphoid tissue
important lymphoid organ and immunologic effector tissue.
Blood
Most frequently sampled lymphoid organ
Blood
Circulating blood has enough mature T cells to produce a (?).
graft-versus-host reaction
In addition, blood transfusions have been responsible for inducing acquired immunologic tolerance in (?).
kidney allograft patients
Found in the mucous membrane lining of the oral and pharyngeal cavities
Tonsils
Tonsils Function:
to respond to pathogens entering the respiratory and alimentary tracts
Function as potential sites for contact with foreign antigen
Appendix
also increases the probability of an immune response along with the other secondary organs
Appendix
T lymphocytes (%) 100
B Lymphocytes (%) 0
Thymus
T lymphocytes (%) 80
B Lymphocytes (%) 20
Blood
T lymphocytes (%) 60
B Lymphocytes (%) 40
Lymph nodes
T lymphocytes (%) 45
B Lymphocytes (%) 55
Spleen
T lymphocytes (%)10
B Lymphocytes (%) 90
Bone marrow
Proteins on cell surfaces can be used as markers to differentiate T and B cells
Surface Markers on Lymphocytes
Proteins can also be used to distinguish the developmental stages of the two types of cells according to when these proteins appear.
Surface Markers on Lymphocytes
Detected by monoclonal antibodies
Surface Markers on Lymphocytes
Specific antibodies made by cloning a single antibody-producing cell
Surface Markers on Lymphocytes
Surface marker that identifies a particular differentiation lineage recognized by a group of monoclonal antibodies
Clusters of differentiation (CD)
45-58
CD2
Thymocytes, T cells, NK cells
CD2
Involved in T-cell activation
CD2
20-28
CD3
Thymocytes, T cells
CD3
Associated with T-cell antigen receptor
CD3
role in TCR signal transduction
CD3
55
CD4
Helper T cells, monocytes, macrophages
CD4
Coreceptor for MHC class II; receptor for HIV
CD4
58
CD5
Mature T cells, thymocytes, subset of B cells (B1)
CD5
Positive or negative modulation of T and B cell receptor signaling
CD5
60-76
CD8
Thymocyte subsets, cytotoxic T cell
CD8
Coreceptor for MHC class I
CD8
100
CD10
B and T cell precursors, bone marrow stromal cells
CD10
Protease; marker for pre-B CALLA
CD10
50-80
CD16
Macrophages, NK cells, neutrophils
CD16
Low affinity Fc receptor, mediates phagocytosis and ADCC
CD16
> 120
CD19
B cells, follicular dendritic cells
CD19
Part of B cell coreceptor, signal transduction molecule that regulates B-cell development and activation
CD19
145
CD21
B cells, follicular dendritic cells, subset of immature thymocytes
CD21
Receptor for complement component C3d; part of B-cell coreceptor with CD19
CD21
45
CD23
B cells, monocytes, follicular dendritic cell
CD23
Regulation of IgE synthesis; triggers release of Il-1, Il-6, and GM-CSF from monocytes
CD23
55
CD25
Activated T, B cells, monocytes
CD25
Receptor for IL-2
CD25
85
CD44
Most leukocytes
CD44
Adhesion molecule mediating homing to peripheral lymphoid organs
CD44
180
CD45R
Different forms on all hematopoietic cells
CD45R
Essential in T and B cell antigen-stimulated activation
CD45R
175-220
CD56
NK cells, subsets of T cells
CD56
CD94
Not known
CD56
70
CD94
Subunit of NKG2-A complex involved in inhibition of NK cell cytotoxicity
CD94