DESARROLLO INMUNOLOGY 2015
About the killing mechanism of Tc cells (the Kiss of death)
How would you define it?
It is a killing attack deliver by an armed cytotoxic T cell previously sensitize by the same antigen. A single Tc cell can attack many target cells (second amplification of the celular IR), we have to take into account that the contact between cells (during the Kiss of death) is very short in time. This attack ends with the death of infected cells.
How many activating signal needs a T cell to be able of delivering the Kiss of death. Explain details for each signal?
They need 3 signal:
1o→recognition of the appropiate peptide loaded onto a self HLA- class I molecule.
2o→co-stimulatory signal delivered by CD28 bound to its ligand on APC, the B7 molecule.
3o→clonal expansion exerted by the autocrine action of IL-2 bound to α+ β+γ high affinity IL-2 receptor.
Surface phenotype of fully active Tc cells
TCR complex (TCR, CD3 and homodimers o heterodimer, more frecuent homodimers tan heterodimers), CD8, HLA-I and HLA-II, CD28, Fas-L...
1→granule dependent. There are several pathways, nuclear and non-nuclear. 2→Granule independent.
Do all pathways end up in the same killing mechanism (yes or not)? Yes
Name the killing mechanism: apoptosis
Molecules involved in this killing mechanism
Granule dependent pathways: perforins, granzymes and others.
Granule independent pathway: Fas/Fas-L
Explain the phenotipic differences and function of B cells in the stages of development.
Immature B cells:
Phenotype: IgM BCR
Function: live un the bone marrow. If they recognize an Ag, die or become a non- functional (this is the mechanism of acquiring CENTRAL B CELL TOLERANCE).
Mature B cells:
Phenotype: IgM BCR + IgD BCR. IgM and IgD have the same antigen combining site.
Mature B cells patrol the organism, from blood to SLO and back to the blood. These cells represent the mature B cell repertoire. Recognition of antigens takes place in SLO. Only foreign Ags can be recognised.
If recognition takes place a primary immuno response will be mounted starting in a clonal expansion. Many cells of the clone became IgM plasma cells and a few became Memory B cells. Memory B cells do class switch and affinity maturation due to somatic hipermutation.
Memory B cells:
Phenotype: IgG (1 to 4), IgA (1-2), IgE depending on T cell help.
Lorena Jiménez Pinzón
Function: after recognition of the Ag the relevant B cell memory start the secondary immuno response, faster, stronger and more... Secreting the same Ig expressed on its Surface.
The role of the NK un innate immunity
How would you define it?
The function of the NK in innate immunity is to active macrophages with the
vacuolar system infected to help them clear their infection.
How does the NK cells gets to know that the macrophage is infected? Infected macrophages release 3 cytokines for which NK cells have receptors: IL-12 increases in NK IFN-g production and cytolytic capacity.
IL-18 increases in NK IFN-g production.
IL-15 increases NK proliferation.
What is the message for the activation sent by the NK cell to the infected macrophage?
NK cells produce IFN-g, the strongest known macrophage activator.
Does the NK cell kill the microorganisms?. Explain how are they killed.
No, NK cells do not kill the microorganism; macropaheges do with the help of NK. IFN gamma activates the macrophages killing machinery.
Indicate the molecules involved in the killing mechanism. 1→toxic oxygen (superoxid O-, hydrogen peroxide H2O2) 2→toxic nitrogen (nitric oxide NO)
3→antimicrobial peptides (defensins, cationic proteins) 4→enzymes (lysozyme)
Can any NK type of NK cell help infected macrophages?
No, only NK bright can do it, that is, those expressing a high concentration of
The heavy chain constant región of immunoglobulins may be related to (mark yes or no).
Lorena Jiménez Pinzón
Affinity for the antigen
Activation of classical complement pathway?
Activation of alternative complement pathway?
Passage from mother to fetus?
Passage from blood to tissues?
Reaction of immunoglobulins with some Fc receptors
Passage from blood to secretions
DESARROLLO INMUNOLOGY 2017
Define isotype, idiotype and allotype
Isotype→it is related with Ig differention. In this case isotype define the different types of constant regions that exist, both in heavy and light chains of Ig. Constant region of the heavy chain is coded in chromosome 14, and it has 9 different isotypes: IgG (from 1 to 4), IgA (1-2), IgD, IgM, IgE. Then the constant region of the light chain could be coded in chromosome 22 for lambda chain and in chromosome 2 for kappa chain, so there are 2 isotypes for constant region of light chain.
Idiotype→it is related with information inherit from our parents, depending on the information inherit Ig will be different, that is the reason why siblings do not have the same capacity of producing Ig, even though they can produce them, the frequency or the amount of them will be different.
Allotype→it is related with the variable region of the heavy and the light chain. There are many different one, more or less 1 for every antigen that exist. We have to remember that it must exist at least one variable chain which recognise an antigen.
Negative and positive selection
Both are related with the capacity of recognition of MHC molecules (class I or II) which are going to be joined to self-peptides in their grooves.
Positive selection→ TCR has to recognise HLA joined to the correct peptide. T cell will express in their membrane the two co-receptor (CD4 and CD8) that is why they could recognise HLA class I or class II molecules. Once they have recognise the HLA molecule with self-peptide, for example HLA-I. CD8 co-receptor is going to join to alfa3 chain of the HLA-I, so CD4 will be silenced. Since the molecule has been recognise, the death pathway for T cell will be avoided.
Finally this T cell in the future is not going to recognise any HLA class molecule other than class I, which is the one they have first recognised.
Negative selection→T cells which have passed the positive selection have to pass the second “exam”. In this case they do not have to recognise self-antigens from HLA molecules. If the TCR of the T cell join to any HLA molecule with high affinity, cellular death will occurred. The reason for not recognising this molecules is not to recognise self-antigens in the future, what can provoke autoimmune disorders.
How can our immune system recognise carbohydrates?
As we know, HLA molecules cannot recognise antigens if they are not proteins (peptides to be more exact). So carbohydrates are not going to be recognise either, however it exists a laboratory process which allow HLA molecules recognise carbohydrates antigens.
The way of doing this is: the carbohydrate has to be joined to a protein. The antigen will be engulfed by B cells, and will be digested inside it by the vacuolar system. Since HLA cannot bind carbohydrates (only peptides), the rest of the protein the carbohydrate was joined to, is going to bind to the Groove of the HLA molecule to be presented to T cells (CD4 or CD8 depending on the receptors and on the type of HLA). When the peptide is recognised, some cytokines will be released and they will advise the B cell to produce antibodies.
When a second recognition of the antigen take place, the Ab formed will be the same as the one formed in the first recognition (the one which recognised the carbohydrates).
Lorena Jiménez Pinzón
The conclusion is that antibodies can be produced against a non-protein antigen, provided that a protein is linked to it. Injecting them together in the same syringe is not enough; They have to be chemically linked! This linkage ensures that it is the same B cell that encompasses the Ag protein complex and presents the resulting peptides to the T cells. (ver pag 76 apuntes español ordenador)
4. Differences between NK dim and NK bright.
We have to take into account that NK cells can participate in innate immune response, and also in adaptive immune response, in the last case, two phenomenon can occur: the ADCC and the destruction modulated by HLA.
DESARROLLO INMUNOLOGY PREGUNTAS SUELTAS
1. The mononuclear phagocytic system
What is it?
A network of cells located in most organ and tissues of the body with 3 main features:
They derived from blood monocytes.
They are phagocytic
They have one single nucleus (neutrophils do not belong to the MPS, they are
Cells belonging to this system
Alveolar, splenic, serosal and lymph node, macrophages, mesangial phagocytes, tissue histiocytes, sinovial A cells, liver kupffer’s cells, bone osteoclasts, microglia, monocytes.
What is their function?
Phagocytosis: triggered by activations of their pattern recognition receptors (manose-fucose receptor, scavenger receptor, 7 transmembrane alpha hélix receptor) and complement receptors (CR1, CR3 and CR4). Toll like receptors are an exception since their activation does not induce phagocytosis.
Does this system belong to the innate or to the acquired immunity?
Basically this system belongs to the innate immunity (no B cell, or T cell involved). Nonetheless some of these cells can process antigens and present the resulting peptides to T cells. In this respect these cells belong to both the innate and the acquired immune system (i.E dendritic cells)
Lorena Jiménez Pinzón
Its morphology is defined as large granular lymphocytes, which do not express the CD3 marker and express the CD16 and / or CD56 molecules. The expression of the CD16 and CD56 molecules is variable among the different subpopulations of NK cells and allows their classification. The following subpopulations of NK cells have been described
• NK dim: CD56dim, comprising about 90% of NK cells, of which a small majority express CD16 and KIR receivers
• NK bright: CD56bright, which do not express CD16 and have low expression of KIR receptors
DESARROLLO INMUNOLOGY OTRO EXAMEN
What are they?
Structure present on the surface of certain immune cells that can recognise the
constant region of certain Igs.
Fc receptors are clasificated depending on the Ig isotype they recognise: (IgG, IgA, IgE). There are subtypes. There are no Fc receptor for IgM or IgD.
They are expressed in different cells and that determines their function.
Another difference is the affinity with which they recognise the Fc region: the highest affinity is for Fc receptor present on mast cells mediating allergic reactions.
The concept of kd and the its clinical relevance
The affinity of the Fc receptor for the Fc region is expressed as a Kd. Example: Kd for FC-IgE is 10^..M the lowest of all Fc receptor. That means that IgE and Fc receptor (epsilon) bind with the highest affinity and that has implications in allergy.
The function of the Fc receptor depend on the function carried out by the cell expressing the receptor. For instance: the Fc (epsilon) R mediate allergic reactions because this receptor is express on mast cells that participate in allergy. In NK cells they mediate ADCC and phagocytes mediate phagocytosis.
Fc receptors are composed of one or several transmembrane peptides. When the cytoplasmic tail is long enough the peptides themselves can transmit the signal to the cell (as in Fc gammaRII). When the cytoplasmic tail is too short another transmembrane molecule transmits the signal, as is the case of any other Fc receptor.
Pattern recognition receptors
How would you define them?
They are structures expressed by the phagocytic cells that recognize not isolated
molecules but molecules organized in particular patterns.
- 7 transmembrane alpha helix
- Toll-like receptors
Receptor for complement factors and Fc receptors are not pattern recognition receptors.
The manose/fucose: molecular patterns with these monosaccharides. The scavenger receptor: recognises anionic polymers. 7 transmembrane alpha helix receptor: a variety of structures (C5a, IL-8, lipid mediator of inflammation such as prostaglandins and leukotrienes) an N-formil methionine peptides. There are different TLRs. The ligand for TLR4 is the lipopolysaccharides (LPS) produce by G- bacteria.
Lorena Jiménez Pinzón
TLRs induce phagocytosis up on recognition of their ligands.
TLR are an exception. They do not induce phagocytosis. The best know (TLR4) induce the production and release of TNF, a cytokine, in response to LPS.
Summary of events in the alternative pathway of complement its biological significance:
Negative selection in T cell maturation. Explain what is it and the role of AIRE gene.
Negative selection takes place in the thymus medulla in thymocites that have passed positive selection in the thymus cortex. Therefore their TCR can recognize self HLA molecules (HLA-I or HLA-II) and will use the corresponding correceptor (CD8 or CD4, respectively) but not both.
The aim of negative selection is to eliminate self-reactive T cells before they enter the circulation and secondary lymphoid organs where they could initiate immune reactions to self- components (autoimmunity).
How does it happened: APC will present via HLA class I molecules peptides to CD8 T cells. If TCR recognizes the peptide/HLA-I complex apoptosis will ensue (CD8, class-I negative selection). The same happens for CD4 T cells that can recognize a peptide/HLA-II complex (CD4, class II negative selection). Only lymphocytes with a TCR that cannot recognize any HLA/peptide complex will survive and migrate periphery..
Up to relatively recently this was the only knowledge .... To explain central tolerance to self-antigens.
The AIRE gen codes for a protein that serve as.... Of many nuclear factor so that more than 1000 ge... To be activated coding for self-proteins that are... To T cells undergoing negative section...Those self-molecules are eliminated by apoptosis