Lecture 34 - T cells Flashcards
MHC-I antigen processing
Antigenic proteins are degraded in cytoplasm
Peptide loading of MHC-I takes place in the endoplasmic reticulum (ER)
MHC-II antigen processing
Antigenic proteins are degraded in acidic phagolysosome
Peptide loading of MHC-II takes place in phagolysosome
T cells
T cells are lymphocytes that arise in the bone marrow and fully develop in the thymus
T cells express T cell receptor (TCR) with co-receptors (either CD4 or CD8)
Recognise MHC/peptide complexes (sense the MHC peptide complexes on the surface of dendritic cells) (MHC are the protein complexes on the dendritic cell that presents the peptide)
These cells have evolved to give us memory to respond to vaccine and be more vigorous to an infection the second time around
Production of T cells
Occurs in the bone marrow, from stem cells and in the bone marrow these are young T cells and they are not functional at this stage and then they migrate via the blood to the thymus
T cell development
T cells migrate from the bone marrow via the blood to the thymus. The thymus is the site of T cell development and TCR (T cell receptor) rearrangement. T cell rearranges its DNA and a small part of the genome is rearranged in response to signals in the developing T cells so all T cells are different from one another in terms of the receptors. At the thymus the T cells learn how to respond appropriately to antigens within the thymus
The T cells then travel to lymphoid organs, blood and tissues
Thymus
T cells develop in the thymus which is located in the upper anterior part of your chest directly behind your sternum and between your lungs.
T cells express a unique T cell receptor
Immature T cells (TCR genes in germline state) in bone marrow. TCR gene rearrangement in the thymus (random but in a defined way therefore there is a lot of diversity in the T cell population). Mature T cells expressing unique antigen receptors (TCR)
Thymic gene rearrangement
Immature T cells (thymocytes) rearrange the ‘cariable’ parts of their TCR genes in the thymus
The rearrangement process is essentially random
This ensures that individual T cells are unique in terms of their TCR. Creates ‘diversity’ in T cell repertoire and this therefore enables recognition of many different microbes
The upper tip of the TCR is rearranged genetically in the thymus which is why we have an adaptive immune system because of the variety of shapes
T cell receptor
The T-cell receptor (TCR) is a protein complex found on the surface of T cells, or T lymphocytes, that is responsible for recognizing fragments of antigen as peptides bound to major histocompatibility complex (MHC) molecules.
T cells express a TCR that recognises peptide+MHC
CD4 and CD8
CD4 and CD8 are ‘co-receptors’ on T cells
CD4 T helper cells
Recognises MHC-II/peptide i.e. respond to antigens normally bought from the outside (the phagolysosome pathway)
Helps CD8 T cell become cytotoxic
CD4 T cells help B cells make antibody
In the lymph node or spleen
CD8 T cells
Recognise MCH-I/peptide
Develops into ‘cytotoxic lymphocyte’ (CTL) aka cytotoxic T cell
CD8 T cells become cytotoxic and kill virus infected cells and cancer cells
T cell differentiation
T cells that have not been activated by MHC/peptide are naive (havent seen antigens)
Activated T cells are also known as effector T cells (experience comes from being exposed to antigens)
Cytokines
Cytokines are produced by CD4 T cells help CD8 cells become activated therefore allow them to do their job
General term for mediators that influence cell development, differentiation and responses in the immune system
Cytotoxic lymphocytes (cytotoxic T cells)
Cytotoxic T lymphocytes (CTLs) represent one of several types of cells of the immune system that have the capacity to directly kill other cells. They play a major role in host defense against viral infection, as well as infection by other intracellular pathogens that replicate in the cytoplasm of the host cell.
Developed from CD8 T cells by exposure to cytokines
