21 17-19 Flashcards
C+C Class I and Class II MHC
DISPLAYED BY All nucleated cells APC
RECOGNIZED BY Naïve CD8/Tc CD4
FOREIGN Ag Endogenous — Exogenous
MESSAGE Kill Me/if Tc, look at what I found — Mount an attack
CD4
Usually become helper T cells that help activate other B cells, other T cells, macrophages and direct the adaptive immune response. A couple become regulatory T cells. Bind only to class II MHCs
CD8
Become cytotoxic T cells that destroy any cells in the body that harbor anything foreign. Bind only to Class I MHCs.
C+C T cells and B cells first lambs
FUNCTION Intracellular patho—Extracellular patho
IMMUNITY cell mediated—humoral mediated
RECEPTOR TCR—antibodies
SECRETORY PRODUCTS Cytokines–Antibodies
TERRITORY Infected body cells—-Blood/Lymph
LIFE SPAN Long——-short
ACTIVE CELLS Th/Tc/Treg——plasma cells
MEMORY yes——yes
BIRTHPLACE Bone marrow——Bone marrow
SCHOOL Thymus——Bone marrow
Cell-mediated immunity
Immunity conferred by activated T cells which directly kill infected of cancerous body cells and release chemicals that regulate the immune response.
T cells can only recognize?
Antigens displayed on APCs
Dendritic cells can display antigens on both?
MHC I and MHC II
What is the stimulus for clonal selection and differentiation of T cells?
Binding of antigen and co-stimulation
2 step process of T cell activation
- Double recognition
CD4 cell recognizes antigen-MHC complex. Both the TCR and CD4 proteins bind to it.
- Co-stimulation - must also bind one or more co-stimulatory signals. (i.e dendritic cells sprout B7 proteins on their surfaces when innate defenses are mobilized)
If the signal is not received, the T cell becomes tolerant/wont divide/won’t secrete cytokines to that antigen (unresponsive = anergy)
Without this safeguard, MHC I proteins that are displaying peptides from within the cell could activate cytotoxic T cells leading to damage of healthy cells.
Proliferation and Differentiation of T cells
When activated by antigen and co-stimulation, a T cell proliferates becoming memory cells and effector cells. Cytokines released by APCs or Ts promote the process.
Cytokines
Language of immune system - mediate cell development/differentiation/responses of immune system.
Includes Interleukins and interferons.
Interleukin I
source: macrophage
Activity: Activation of T cells and macrophages, promotion of inflammation and fever
Interleukin II
Source: Helper Ts
Activity: Activation of lymphocytes, NK cells and macrophages
Roles of Helper T cells
Stimulate proliferation of other T cells and B cells that are bound to antigens.
- Activation of B cells
- Activation of CD8 cells
- Amplification of Innate defenses
- Subsets of Th cells
How do helper cells help in humoral immunity?
Th cell binds with a B cell that has encounted its antigen and is displaying it on MHCII.
Th cell releases interleukins as co-stimulatory signals to complete B cell activation.
How do helper cells help in cellular immunity (with CD8)?
- previously activated Th cell binds to a dendritic cell.
- Th cell stimulates dendritic cell to express co-stimulatory molecules needed to activate CD8 cell.
- Dendritic cell can now activate CD8 cell with the help of interleukin 2 secreted by Th cell.
How do cytotoxic cells work?
- Tc binds tightly to target cell when it identifies foreign antigen on MHC I protein.
- Tc releases perforin and granzyme molecules from its granules by exocytosis.
- Perforin molecules insert into the target cell membrane and form a hole. Granzymes enter the target cell via the pores. Once inside they degrade cellular contents stimulating apoptosis.
Cellular immunity flowchart - CD4
Ag infected body cell engulfed by dendritic cell becomes APC –>
activates naïve CD4 –>
clones give rise to memory and helper T –>
2 processes:
- Helper T cytokines stimulate nonspecific killers (macrophages and NK cells of innate sys.)
OR
- Helper T cells co-stimulate and release cytokines in response to B cells that present Ag to helper cell This causes an increase in B cell division.
Cellular immunity flowchart - CD8
Ag infected body cell engulfed by dendritic cell becomes APC –>
activates naïve CD8 –>
clones give rise to memory CD8 and Cytotoxic T cells –>
together the nonspecific killer (macrophage/NK) and cytotoxic T cells attack the Ag
What are CD4 and CD8s?
cell differentiation glycoproteins
Distinct from antigen receptors!
MHC restriction
CD4 cells are restricted to binding antigens only on class II MHC
CD8 are activated by fragments on MHC I and after activation look for the same antigen on class I MHC located on any cells of the body.
