Photorespiration is very low in C4 plants and the quantum yield does not

show a temperature dependence.

TLS Online TPP Program

#Id: 1762

#Unit 4. Cell Communication and Cell Signaling

Central tolerance deletes self-reactive T- or B-cell clones before the cells are allowed to mature. occurs in the primary lymphoid organs

TLS Online TPP Program

#Id: 1763

#Unit 4. Cell Communication and Cell Signaling

Peripheral tolerance, which renders some self-reactive lymphocytes in secondary lymphoid tissues inactive and generates others that actively inhibit immune responses against self

TLS Online TPP Program

#Id: 1764

#Unit 4. Cell Communication and Cell Signaling

Self antigens are not uncommon in the periphery, Two factors contribute to this:                                                                                                                             a. not all self a. antigens are expressed in the central lymphoid organs where negative selection occurs

b. there is a threshold requirement for affinity to self antigens before clonal deletion is triggered, allowing some weakly self-reactive clones to survive the weeding-out process.

TLS Online TPP Program

#Id: 1765

#Unit 4. Cell Communication and Cell Signaling

The possibility of damage from self-reactive lymphocytes is further limited by the life span of activated lymphocytes, which is regulated by programs that induce cell death (apoptosis).

TLS Online TPP Program

#Id: 1766

#Unit 4. Cell Communication and Cell Signaling

Activated T cells express increased levels of Fas and FasL. In both B and T cells, engagement of Fas by FasL induces a rapid apoptotic death known as activation-induced cell death (AICD).

TLS Online TPP Program

#Id: 1767

#Unit 4. Cell Communication and Cell Signaling

Tolerogens- Antigens that induce tolerance