Regulation of the Immune System- L11 Flashcards
Tolerance
Lack of response to a specific antigen
2 major mechanisms of tolerance induction
- Deletion of reactive cells
2. Inactivation of reactive cells: Anergy
Clonal deletion in T cells
- Occurs in thymus
- Tight association of autoreactive TCR to MHC presented antigen on thymic dendritic cells causes apoptosis
Clonal anergy in T cells
T cells become inactivated if an appropriate co-stimulatory signal is not received
Generation of T regs
Active process, suppresses autoreactivity
Mechanisms of tolerance in T cells
- Clonal deletion
- Clonal anergy
- Functional deletion
- Generation of suppressor or T reg cells
- Blocking of presentation or activation
Mechanisms of tolerance in B cells
- Clonal deletion
- Clonal abortion/clonal anergy
- Functional deletion
T regs
FoxP3+CD25+CD4+T cells that actively suppress pathological and physiological immune responses
IPEX
Syndrome where FoxP3 is lost and T regs cannot differentiate. Patients with IPEX develop many autoimmune disorders.
Mechanisms of regulation by T regs
- Direct contact with target cells
- Cytokine mediated suppression of T cells
- Cytokine mediated suppression of pAPC function
B7:CTLA4
Stop signal for T cells, binding inactivates them
CTLA4 expressed by T cells, B7 by APCs.
Protein antigens can induce
- Humoral immunity
- Cell mediated immunity
- Class switching
- Affinity maturation
- Generation of memory cells
Polysaccharide and lipid antigens can induce
- Humoral immmunity
- Can NOT induce CMI
- This is why we don’t have long-lived immunity to encapsulated bacteria!!!!
How can antibody itself regulate the immune response?
- It can sequester antigen and prevent other B cells from being activated by it
- Can cross link Ig and Fc receptors to inactivate
Ex: preventing an Rh response
