Chapter 9 Flashcards
MHC class I
Present on the surface of all nucleated cells.
MHC class II
Present on the surface of all professional antigen presenting cells.
Antigen Presenting cells
Dendritic, Macrophages, and B cells. Dendritic cells and Macrophages pick up antigens at infected area.
Dendritic cells
They function by processing antigen material and present it on the cell surface to the T cells of the immune system. They act as messengers between the innate and the adaptive immune systemsOnce activated, they migrate to the lymph nodes where they interact with T cells and B cells to initiate and shape the adaptive immune response.
Antigen processing
Antigens processed for MHC proteins to display epitopes. Different processes for endogenous and exogenous antigens.
Processing of endogenous antigens (MHC I)
Antigens from endogenous pathogens, such as virus, are processed by endogenous pathway, in which the proteasome degrades the antigen into smaller peptides, which are transported to the endoplasmic reticulum. In the ER the peptide is attached to a MHC class I molecule and delivered to the cells surface for presentation to a CD8+ T cell.
Processing of exogenous antigens (MHC II)
Exogenous antigens are taken into the cells by a phagosome, joined to an MHC class II molecule, and taken to the cells surface for presentation to a CH4 T cell.
Cell-mediated Immune responses
Respond to intracellular pathogens and abnormal body cells. The most common intracellular pathogens are viruses. The response is also effective against cancer cells, intracellular protozoa, and intracellular bacteria. Effector cells are the cytotoxic T cells (CTL) expressing CD8.
Activation of a clone of cytotoxic (CD8+) T cells
Antigen presenting cells present antigen to naive cytotoxic lymphocytes by linking the antigen to MHC-I molecule which is recognized by CD8 molecule on the surface of cytotoxic T cells.
Killing by activated cytotoxic lymphocytes
1) Virus infects cell
2) Cell expresses viral antigen
3) Infected cell is killed by cytotoxic T cell by activation of nuclease that cleaves host and viral DNA
Cytotoxic lymphocytes (CTLs) kill using 2 primary mechanisms
Perforin-Granzyme Cytotoxic pathways and CD95 pathway.
Perforin-Granzyme Cytotoxic pathway
T-cell sits on virally infected cell, then releases vesicles with perforin that forms pores on the infected cell, another vesicle with granzyme enters through the pores made by the perforin and once inside causes the cell to apoptosis.
CD95 cytotoxic pathway
CD95 receptor is presented by the host cell and then the Cytotoxic T cell presents a ligand CD95L which interacts and activates with the CD95 receptor. This activates the apoptosis pathway.
Memory T cells
Some activated T cells become memory T cells. Persist for months or years in Lymphoid tissue. Immediately functional upon subsequent contacts with epitome specific to its TCR.
Humoral Immune responses
Adaptive responses mounted against exogenous pathogens. Provides the soluble component of adaptive immunity (humors).
T-independent activation of B cells
Does not require T cell help. T-independent antigens can directly stimulate the B cells to produce antibody without the requirement for T cell help In general, polysaccharides are T-independent antigens.
T-dependent activation of B cells
Requires signals provided by T-helper cells. Most important. Antigen presenting cells stimulate CD4 T cell to become an effector Th1 or Th2 cells. Th2 cells then activate B cells.
Process of B cell activation
1) B-cell binds to virus through viral coat protein
2) Virus particle is internalized and degraded
3) Peptides from internal proteins of the virus are presented to the T cell, which activates the B cell.
MHCII binds with the CD4 on the T cell as well as CD40 binding to CD40L. Once binding is over the Th2 cell releases IL-4 which activates the B cell to start producing antibodies (AgM).
Plasma Cells
Majority of the cells produced during B cell proliferation become plasma cells. Initial plasma cells produce large quantities of antibodies in lymphoid tissues (IgM). Individual plasma cells are short lived.
Plasma cells in the germinal center
Cells with improved binding to Ag will replicate (affinity maturation), undergo class switching (to IgG) and become plasma cells, unimproved cells will die. IgG secreting plasma cells migrate to the bone marrow and are long lived
Memory B cells
Produced by B cell proliferation but do not secrete antibodies. Have BCRs complementary to the antigenic determinant that triggered their production. Long-lived cells that persist in the lymphoid tissue. Initiates antibody production if antigen is encountered again.
Primary response
3 day lag period. Initially produces IgM then produces IgG
Secondary response
Once antigen encountered quickly starts producing IgG and IgM. Produces more IgG.
