Lecture 2 Flashcards
Why do lymphocytes enter G1 phase?
d/t stimulation, they are activated lymphocytes called large lymphocytes of lymphoblasts
What lymphocytes are in the G0 phase?
Naive and Memory cells- resting lymphocytes. Not actively dividing or performing effector functions.
Survival of naive Lymphocytes depends on what?
Signals generated by Antigen receptors TCR or BCR or Cytokines
How to antigen receptors of naive BCR’s survive?
They generate survival signals even in the absence of antigen
How do naive TCR receptors survive?
Naive TCR recognize self antigens weakly enough to generate survival signals but without triggering clonal expansion and differentiation into effector cells.
What is the most important cytokine for naive T cell survival?
IL-7 promotes low level cycling of naive T cells
What cytokine belonging to the TNF family is required for B cell survival?
BAFF- B cell activating factor
The cell to cell interaction of T cells with specialized epithelial cells, DC’s and M0 cell in the thymus provide mechanisms for what?
Selection, and differentiation of T cells useful to the immune system.
What are immune system messengers?
Cytokines
What Cytokines are important in T cell development?
IL-1,2,6,7
Following migration from the Thymus, Naive T Cells-
are maintained in the periphery with out proliferating
Where are Antigen specific T cells produced
in the Thymus from circulating T cell precursors derived from stem cells in bone marrow
Each T cell has receptor specific for how many antigens?
One- generated by gene rearrangement from multiple inherited germline genes
T cells undergo selection to do what?
Remove those that are self reactive
T helper cells express what?
What is the function?
Cd4
To provide help for B cell growth and differentiation
Cytotoxic T cells express what?
What is it’s function
CD8
To recognize and kill virus infected cells
Mature T cells migrate where?
To do what?
To secondary lymphoid tissue
To mediate protection
B cell development starts where in the fetus and continues where after birth?
in the fetal liver at 14 weeks gestation and after birth in the bone marrow
What cytokines are important for B cell development?
Contact with Stromal cell and IL-1,6,7
Where are BCR’s encoded for recognition of antigen?
in bone marrow
Do B cells recognize more than one antigen?
No B cells are generated each with a unique specificity for a particular antigen.
BCR’s that react with self antigens are eliminated,
B1 and B2 develop with different properties, What is the first Antibody expressed on B cells and what is the second?
IgM is first expressed as the BCR and then IgD.
Mature B cells migrate where?
Secondary Lymphoid tissue where they respond to foreign antigens.
What happens when B cells are activated by an antigen?
They proliferate in germinal centers and mature into memory and plasma cells. Plasma cells are terminally differentiated B cells which produce and secrete large amounts of antibody
How do B and T cells interact?
B cells present antigens to helper T cells which is a key step in cooperation of T helper cells with B cells for antibody responses to protein antigens
Lymphocytes circulate everywhere except?
Brain, Eyes, Testicles.
HVEC’s allow lymphocytes to enter where?
Skin, intestines, and lymph nodes
HEV’s function to do what?
Express high levels of adhesion molecules that serve as homing receptors for lymphocytes in response to chemokines- lymphocytes migrate by diapedesis into tissue
How do lymphocytes reenter circulation?
Via efferent LN’s that merge into the thoracic duct
Where do naive lymphocytes go?
- Respond to foreign bodies in secondary lymph tissue
2. Return by lymphatic drainage and recirculate through other secondary organs
What are the steps of lymphocyte activation?
- Fully mature naive T cells and immature B cells migrate to 2 lymph organs 2. B cells complete maturation in LN and spleen 3. Naive B and T activated by Antigens and differentiate into effector or memory lymphocytes 4. Some effector or memory lymphocytes migrate into peripheral tissue sites of infection 5. Antibodies secreted by effector B cells in LN and spleen and bone marrow enter the blood and are delivered to sites of infection
What are APC’s
Cells that capture process and display microbial antigens to lymphocytes and provide signals that stimulate the proliferation and differentiation of lymphocytes
What cells are considered APC’s
Macrophages and B cells present antigens in cell mediated and humoral
Dendritic cells- Major APC
What type of cell relies on APC’s
Mostly T cells, B cells do not need APC for activation
Follicular Dendritic Cells display what?
B cells during phases on humoral immunity
what provides a link between innate and adaptive immunity?
Dendritic cells and macrophages because they are used in both
What do Dendritic cells do and what lineage are they from?
Important for T cell activation, phagocytic capabilities
Derive from myeloid lineage
What is dendritic cell maturation dependent on?
FLT3 ligand which binds to FLT3 Tyrosine Kinase receptors on the precursor cells.
Activated DC’s secrete what?
Cytokine
Macrophages and Dendritic cells express receptors that recognize Antigens typically made by what?
Microbes and not mammalian cells
Classical DC’s reside where?
Skin, Mucosa and organ parenchyma
How are Classical DC activated?
By microbes- they migrate to LN’s where they display microbial protein antigens to T lymphocytes
What is the function of Plasmacytoid DC’s
Early responders to viral infections they recognize nucleic acids of intracellular viruses and produce soluble proteins Type I interferons aka IFN alpha/beta that have potent antiviral activities
During an inflammatory response DC’s may also come from where?
circulating monocytes
