immunology - ksu
TRANSCRIPT
Immunology
Lecture- 5
Adaptive Immunity
T- cell
Cell Mediated Immunity
• An adaptive immunity mediated by response specific cells of immune system, that recognize foreign
antigens on the surface of cells, organisms or tissues.
• T cell have an antigen receptor that recognize and react to a specific antigen ( T cell receptor)
• Requires constant presence of antigen to remain effective
- Involves cytokines
T lymphocytes ( T- cell) ( The main agent of cellular immunity)
Helper T cell Cytotoxic T cell
• T-cell do not produce antibody but instead attack foreign antigen directly
• T cell regulate the proliferation and activity of other cells of immune system: B cell, macrophages,
neutrophil and natural killer cells
• Each type of T cell
• Respond to different types of antigen presenting cells ( dendritic cells, macrophages, B cells) • Activated by different antigen presentation • has different effector function
T- Cell
• Principle function of T cells
• response and eliminate intracellular pathogen and expressing foreign antigens.
• Eliminate tumor cells
• Native T cell circulate between blood stream and the lymphatic system
• Native T cell response only to Antigen presenting cells.
Cell-Mediated Immunity – T Cells
- T cells bind to small fragments of antigens that are bound to normal cell-surface proteins called MHC
molecules
- Infected cells produce MHC molecules which bind to antigen fragments and then are transported
to the cell surface in a process called antigen presentation
- A nearby T cell can then detect the antigen fragment displayed on the cell’s surface
- Depending on their source peptide antigens are handled by different classes of MHC molecules
- Antigen activates effector T cells and produces memory T cells and cytotoxic T cells that lyse virus-
infected cells, tumor cells
Antigen Recognition
- Lymphocytes respond to antigens bound to either class I or class II MHC proteins
- T cell membranes contain CD markers
- CD3 markers present on all T cells
- CD8 markers on cytotoxic and suppressor T cells
- CD4 markers on helper T cells
T- cell receptors
T cell
• Induction of cell mediated immunity : Depend on nature of antigenic stimulus
• Defenses against
• Best develop after following infection by Bacteria and viruses that are inside host cells (
intracellular) and are inaccessible to antibodies.
• Fungi, protozoa
• Tumor cells
• Live vaccine highly stimulus
• Killed vaccine not very effective but effective if contain adjuvant
Types of T cells
Major types of effector T cells
• 1- Cytotoxic T cells
• (attack foreign cells) Recognize antigen on surface of virus infected cells , tumor cells, allograft
cells with MHCI and sectored lymphokines and destroy target cells.
• Kill infected host cells that bear a foreign antigen on contact.
• Directly kill certain cells; Cells infected with viruses and other intracellular pathogens Abnormal
(tumor ) cells
• Distinguished by the CD8 cell-surface glycoprotein
• may possess fc receptors for IgG. It functions by killing target cell through antibody-dependent cell-
mediated cytotoxicity or through perforin formation, killing cells without prior sensitization
• Produce cytokines, which promote phagocytosis and inflammation.
Cytotoxic T cells
Types of T cells • 2- Helper T cells
• Stimulate ( help) B cells to produce antibodies.
• produce cytokines; secrete interleukin 2 (I-2) which stimulates cell division of T cells and B cells (recruit even
more cells to help fight the pathogen).
• Induce formation of cytotoxic T cells.
• Most are CD4 (identifier- forming part of larger structures such as the T-cell receptor)
• Recognize antigen on the surface of antigen presenting cells (e.g. activate macrophage)
• serves in the defense against intracellular agents, including intracellular bacteria (eg, mycobacteria), fungi,
protozoa, and viruses.
• 2 types • Type 1 helper T cell (TH 1) • Assist cytotoxic T cells • Express CD26 and a cytokine receptor named CCR5
• Type 2 helper T cell (TH 2) • Assist B cells • Have cytokine receptors CCR3 and CCR4
Helper T Cell
Types of T cells
3- Suppressor T cell - ( regulatory T cell)
- inhibit the activation of T and B cells
- regulate immune response
- suppress induction of effector T cells ( autoimmune disease, organ transplantation)
- inhibiting, suppressing, or helping to stop an immune response by releasing signals to other immune cells.
Types of T cell
• 4- Memory T cells • jump- start an immune reaction upon re-infection.
• function during a second exposure to antigen
• These cells remain dormant after the initial exposure to an antigen. If the same antigen presents
itself again, survive a long time (even if it is years later).
• the memory cells are stimulated to convert themselves into cytotoxic T cells and help fight the pathogen.
• Can stimulate memory B-cells to produce antibodies
Memory T cell
Major Histocompatibility Complex ( MHC)
Glycoprotein family of cell surface molecules which controls a major part of the immune system.
T cell activation involves recognition of antigens combined with MHC on the surface of cells.
The major function:
bind to peptide fragments derived from pathogens and display them on the cell surface for recognition
by the appropriate T-cells.
MHC molecules mediate interactions of leukocytes
The MHC determines compatibility of donors for organ transplant, as well as one's susceptibility to an
autoimmune disease via cross reacting immunization.
• There are 2 major classes of MHC associated with T- cell function, namely:
• MHC class I: found on all cells
• display antigens on surface of nucleated cells, display peptide antigens to cytotoxic T cells.
• MHC class II: found on phagocytes
• located mainly on dendritic cells, macrophages, and B cells display antigens to helper T cells, resulting in
activation of immune cells
MHC classes
MHC
MHC
Antigen presenting Cell
• Express MHC and can present antigen to the T cells
• Can present antigen to the T cells via a histocompatibility molecule.
• Depending on the antigen presented and the type of the histocompatibility molecule, several types of T cells can become activated.
• For T-Cell Receptor (TCR) recognition, it must be processed into small fragments inside the cell and presented to a T-cell receptor by MHC. Antigen by itself is not capable to elicit the immune response without the help of an Immunologic adjuvant.
• Macrophages
• B- cell
• Dendritic cells
Antigen Presenting cell
T cell and Superantigens
• Reaction has drastic consequences
• Superantigens are a form of a virulence factor
• Provoke overwhelming immune responses by large numbers of T cells
• – Release of cytokines
• – Blood vessel damage
• – Toxic shock
• – Multiorgan damage