Introduction immunology - adaptive immune system - L3 Flashcards
- How do B cells kill pathogens?
- How do CD8+ T cells kill pathogens?
- How do CD4+ T cells kill pathogens?
- B cells: mature B cell expresses membrane-bound immunoglobulin of a single antigen specificity, When a foreign antigen binds to this immunoglobulin, the B cell is stimulated to proliferate. Its progeny differentiate into plasma cells that secrete antibodies of the same specificity as the membrane-bound immunoglobulin.
- CD8+ T cells bind to target cell (e.g. virus-infected cell) and releases cytokines to kill the cell.
- CD4+ T cells can either bind to antigen presenting cell (APC), which leads to secretion of cytokines that aid in the killing of the pathogen within the APC or a CD4+ T cell can bind to an antigen-bound B cell, which causes the T cell to secrete cytokines that aid in the differentiation of the B cell into an antibody-secreting plasma cell.
How does an antigen-presenting cell (APC) present the antigen to other cells such as CD4+ T cells?
Through the use of MHC molecules, located in- and outside the cell.
There are two kinds of MHC classes: MHC class I and MHC class II. What is the difference between them?
- MHC class I is able to interact with CD8+ T cells. MHC class I presents antigens from intracellular pathogens independent of what type of cell the antigen is located in.
- MHC class II is able to interact with CD4+ T cells. MHC class II presents antigens from extracellular pathogens located on antigen presenting cells such as B cells, macrophages and dendritic cells.
MHC molecules are polymorphic. What is meant by this?
MHC molecules come in various allelic forms. This means that everybody expresses a different set of MHC class I and II molecules.
What makes the adaptive immune system adaptive and specific?
That the receptors of B and T cells are variable, meaning that each unique B or T cell recognizes a different (set of) pathogen(s).
T cells undergo a process called positive selection in the thymus by cortical epithelial cells. Describe this process.
T cells with a T-cell receptor (TCR) that binds to a self-MHC class I molecule on thymic cortical epithelial cells, macrophages, and other cells in the thymus are signaled to survive and proceed to negative selection. T cells with a TCR that binds to no self-MHC class I molecules are signaled to die.
What is the process of negative selection of B and T cells?
T or B cells with a receptor that binds too tightly to a self-MHC class I molecule on dendritic cells, macrophages, and other cells in the thymus or bone marrow are signaled to die. T or B cells with a receptor that binds moderately to a self-MHC class I molecule on dendritic cells, macrophages, and other cells in the thymus or bone marrow are signaled to survive, mature, and enter the peripheral circulation.
There are mechanisms to prevent autoimmunity (besides negative selection). Such as:
* natural regulatory T cells
* induced regulatory T cells
Describe these two mechanisms in the prevention of autoimmunity.
- Natural regulatory T cells: are formed in the thymus and are specific for self-antigens
- Induced regulatory T cells: are formed in the periphery and are specific for self- or microbiota antigens.
Regulatory T cells express IL-10 and TGF-B, which are suppressive cytokines. These cytokine produced by the Treg cells inhibit other self-reactive T cells.
When T cells leave the primary lymphoid organ (i.e. the thymus), they are still in an immature stage. How do T cells get activated so that they can help the immune system?
When there is an infection, dendritic cells and macrophages phagocytose the pathogens (innate immunity). With this, the antigens of the pathogen get engulfed and dendritic cells and macrophages can act as antigen-presenting cells (APCs) and get transported to lymph bodes to stimulate the adative immune system by presenting the antigens to T cells for T cell activation. The T cells become effector T cells and travel to the infected tissue.
What is meant with cross-presentation and cross-priming?
- Cross-presentation: when dendritic cells phagocytose an extracellular pathogen, the antigen is presented on the cell-surface by an MHC class I molecule. Normally, MHC class I molecules present intracellular pathogens to CD8+ T cells. Therefore, this way of presenting the antigen to CD8+ T cells is called cross-presentation.
- Cross-priming: the immune response that is initiated by cross-presentation.
Activation of a naive T cell by dendritic cells consists of three signals. Describe these signals.
- Signal 1: antigen presentation by MHC molecule to T cell receptor.
- Signal 2: Costimulation enables proliferation and survival.
- Signal 3: Production of cytokines by antigen presenting cell, i.e. dendritic cell, result in differentiation in specific effector T cell.
What is meant with clonal selection of T cells?
Clonal selection: the expansion of T cell clones that recognize a specific antigen and the differentiation into effector cells.
There are specific subsets of CD4+ T cells, namely: Th1, Th2, Th17, Tfh, and Treg cells. Describe which produced cytokine is characteristic for each T cell type and what their main function is.
- Th1: IFN-y, activates macrophages.
- Th2: IL-4, activates cellular and antibody response to parasites.
- Th17: IL-17, enhances neutrophil response.
- Tfh: IL-21, activates B cells to refine antibody response.
- Treg: TGF-B and IL-10, suppress other effector T cells.
There are five different immunoglobulin isotypes: IgG, IgM, IgD, IgA, and IgE. Which immunoglobulin is expressed by naive B cells that have been generated in the bone marrow?
IgM and IgD
What happens with B and T cells after they have been generated in the bone marrow (i.e. primary lymphoid tissue)?
B and T cells migrate from the bone marrow (primary lymphoid tissue) to the spleen and other secondary lymphoid tissues by entering high endothelial venules (HEVs) and then migrate to B and T cell areas.
