Adaptive Immune system Flashcards
What is adaptive Immune response?
The adaptive immune response consists of cell-mediated responses and antibody (humoral) responses
What cells drive cell-mediated immunity?
T-cells
describe B cells in terms of adaptive immune system
B cells produce antibodies and drive humoral immunity
What is meant by immunological memory?
Whereby pattern recognition receptors recognize any microbes, T cell and B cell receptors are specific for components of a certain pathogen (eg antigen)
When does the kinetics of adaptive immune system kick in?
> 4-7 days
What is the threshold level of antigen and why is it important?
the “amount” of a pathogen present to mediate an immune response
This is important as the immune system does not need to mediate adaptive immunity if only a small amount of antigen present – e.g., innate immunity can clear the threat without help of adaptive immunity
What are the three main receptors in adaptive immunity?
T cell Receptor (TCR)
B cell Receptor (Immunoglobulins[Ig])
Major histocompatibility complex (MHC proteins)
T cells are derived from bone marrow however where do they mature?
Thymus
What do T-cells give rise to?
cellular immunity
What are the main types of Tcell receptors circulating?
alpha and beta chains
(beta and delta more uncommon-5%)
What two gene segment codes for the alpha chain?
V&J (variable and joining)
What three gene segment codes for Beta chain?
V,D, J (variable, diversity and joining)
What region has multiple antigen binding sites and can change shape (recombination)?
Variable region
What are the two types of selection when Tcells interact with thymic cortical epithelial cells?
Positive selection, negative selection
what is positive selection of T-cells?
No recognition = apoptosis
What is negative selection of T-cells?
Recognition of self antigen = apoptosis
What do all T cells start as?
Naive cells
What are the three signals required for activation and determining fate of T-cells?
1’ MHC-TCR interaction
2’ co-stimulatory molecules interactions (CD80/CD86 and CD40 on DC —- CD40L and CD28 on T cell)
3’ signal dictates what T helper cell the naïve cell become
What enzymes induce target cell apoptosis?
perforin and granzyme
What do Cytotoxic T cells (CD8+) do?
destroy infected host cells by inducing apoptosis
What are B cells?
They produce antibodies and have a specific receptor for antigens
clonal expansion of b-cells results in what two subsets?
plasma cells and memory b cells
Where do B cells mature
bone marrow
What are the three main receptors in adaptive immunity?
T cell Receptor
B cell receptor
major histocompatibility complex
What are the five immunoglobulins produced by B cells?
IgG, IgE, IgD, IgM and IgA
What is a function of IgG?
most prominent antibody in body, resistance of most viruses- 4 subsets
What is a function of IgE?
exposed on surface of basophils and mast cells
What is a function of IgA?
found in glandular secretions- mucus, saliva and tears- 2 subsets
What is a function of IgD?
found on surface of B cells and can bind to antigens in extracellular fluids
B cell receptor
What is the function of IgM?
capable of binding to multiple antigens-blood
What is the B cell receptor structure?
have varible and constant regions (like T)
have light and heavy chains
An immature receptor is mainly what immunoglobulin?
IgM
Describe B cell negative selection
Like the TCR there is great diversity in the B cell receptor repertoire.
Need to ensure that there is no reactivity against self antigens.
B cells undergo negative selection in bone marrow.
Macrophages will engulf and remove self-reacting B cells.
What are the three main functions for antibodies in the human body?
Neutralization
Opsonization
Initiation of complement
What is meant by opsonization?
Opsonisation refers to coating of pathogens by antibodies or complement proteins
Phagocytosis
Antibody dependent cellular cytotoxicity (ADCC)
Mast cell degranulation
in compliment iniitiation what is meant by the classical pathway?
antibody attached to microbe
diversity of antibody specificity involves what?
gene re-arrangements during development
What are the two types of B cell activation?
Thymus-dependent antigen
Thymus-independent antigen activation (no T cells)
Activation of naive B cells results in rise of what?
plasma cells
What is meant by affintiy?
= strength of binding of single antibody to antigen
What is meant by avidity?
ability of antibodies to form complexes
What role do B and T cells play in vaccinations?
Antigen exposure leads to immunological memory.
In the primary immune response IgM acts early but as B cells undergo class switching an IgG response follows.
Presence of memory T and B cells means that upon a second exposure the immune system can respond much faster.
In addition, we have cells that are primed to produce a more effective IgG (rather than IgM) response immediately
what is immunological tolerance?
Sometimes the immune system can become dysfunctional and in a state of immune unresponsiveness to a particular antigen or set of antigens (immune tolerance).
allergies
What signal determines the subset the cell differs into?
third
What does breach of tolerance result in?
self antigens drives many autoimmune disease
