Antibody and cell-mediated effector functions Flashcards
CD4+ T helper (Th) cells
The key to adaptive immunity
- Must be activated by an antigen- presenting DC
- Activated CD4+ T cells activate many responses
CD8+ T cytotoxic (Tc) cells
Must be activated by an antigen-presenting DC
- Activated T cell KILLS the cell presenting the antigen (Ag)
B cells
Recognize antigen directly
- Need help from activated CD4+ T cell to optimize antibodies and for memory
- Activated B cells differentiates to a plasma cell that produces antibodies that recognize the same Ag as the BCR on the mother cell
Th cells
–>cytokines–>indirectly contribute to the activation of phagocytic cells, B cells and cytotoxic T cells Th1, Th2, Th17, TFH, (Treg)
Cytotoxic cells
–> directly attack infected cells and certain pathogens - CD8+ CTL
- NK cells
- NK T cells
Antibody-mediated immunity
Mediated by antibodies secreted
by plasma B cells
Ab
detect antigens from pathogens found in extracellular spaces and
clear infection by;
* Neutralization
* Agglutination
* Opsonization
* Complement activation
* Antibody-Dependent Cell-mediated Cytoxicity
* NK cells
* Antibody-mediated Degranulation and Mediator Release * Granulocytes
Effector T cells:
Activated CD4+ Th cells Cytokines -> activate other cells Aktivert CD8+ Tc cells Cytotoxins -> kill virus-infected cells
Cytokines
– signal proteins
Cytotoxins
– death proteins
Cytotoxic effector cells include three subsets
- Cytotoxic T Lymphocytes (CTL)s
- Natural Killer (NK) cells
- Natural Killer T (NKT) cells
apoptosis
is the process of programmed cell death. It is used during early development to eliminate unwanted cells; for example, those between the fingers of a developing hand. In adults, apoptosis is used to rid the body of cells that have been damaged beyond repair.
Precursor Cytotoxic T lymphocytes need to be activated by
CD4+ Th cells or licensed DC
Precursor (naïve) CTL
In order to be activated, a naive T cell must recognize a foreign peptide bound to a self MHC molecule. But this is not, on its own, sufficient for activation. That requires the simultaneous delivery of a co-stimulatory signal by a specialized antigen-presenting cell
-no high-affinity IL-2R, or IL-2 production
* No cytotoxic activity
Activated CTL
-Expres scytotoxins packaged into lytic granules
* UpregulateIL-2R
* ProduceIL-2(proliferation and differentiation)
Cross-presentation
allows presentation of exogenous antigens on MHCI and priming of CD8+ T cells
Dendritic cells (DC)s primary cross-presenting cell type
Exogenous antigens are redirected to the endogenous presentation pathway
– Allows presentation on MHC class I molecules, priming CD8+ T-cell responses
– Licensed DC are resistent to the cytotoxic effects of Tc.
Antigen presentation to T cells
All cells can present antigen from inside cytoplasm on MHCI
- Signals that the cell is infected or cancerous
- Aktivated CD8 T cells that recognize Ag will kill
cell
Professional antigen-presenting cells
Can take up Ag from outside cell and present on MHCII –Activate CD4+ Th cells
- Can activate T cells without being infected
- Dendritic cells (DCs) -naïve T cells –> activated
T cell
- Macrophage
- Bcell
Exception Cross-presentation
DCs kan present antigen from outside the cell on
MHCI to CD8 T cells without being infected and
without getting killed
-> activate CD8+ Tc cells
Cross presentation activates naïve CTL to become effector CTLs
Naïve Tc must be activated by APC to become effector Tc (CTL)
APC licensing Th1 express CD40L binds CD40 CD80/86 up + cytokines
– CD4+ T cells are required for CD8+ T-cell memory and optimal expansion.
Signal 1
―TCR binds peptide on MHC classI on APC
Signal 2
―co-stimulatory signa lCD28-CD80/86
– APCs get help from Th1\Th17 cells to upregulate stimulation molecules
Signal 3
IL-2–>proliferation and differentiation into CTL form