n vitro, maturation/activation can be induced by a number of stimuli, including cytokines such as TNF-? and/or other cytokines, monocyte-conditioned medium, or CD40 receptor cross-linking. Immature DC comparable to those found in non-lymphoid tissues can be generated by culturing human PBMCs in medium supllemented with GM-CSF and IL-4. These cells have been instrucmental in identyfying the stimuli that induce DC maturation that include IL-1, TNFa, LPS, CD40 ligand (CD40L) and monocyte conditioned medium. 

LPS 

Factors affected by LPS

In comparing immature DCs with mature DCs, gene array analysis has shown that LPS induced maturation of DCs upregulates the following:

Upregulation

Cytokines: moderate increase: G-CSF, IL-12, Flt3L, IFN?R2 and IL-2R?; 

dramatic increase TNF-?, IL-1?, IL-1? and IL-6.

Chemokines: moderate increase: MCP-1, MIP-1? and MIP-1?

moderate increase: RANTES, MIP-2   dramatic: GROa

chemokine receptors: CCR7

Transcription factors: NFkB

Other genes: MMP-13, STRAP

Downregulation

cytokine receptors: TNF?RII, IFN-yR1, IL-10R? and M-CSFR

Chemokines: IGF-1

Chemokine receptors: CCR1, CCR2, CCR5, IL-8R, CXCR4, 

Other genes: RP105, Ax1, and UCP2

LPS signalling pathways 

Importance of MyD88: MyD88 independent pathway downtream of TLR can lead to functional maturation of DCs. MyD88 dependent and independent pathways originate at the intracytoplasmic region of TLR4, because both cytokine induction and functional maturation are abolished in CDs from C3H/HeJ mice carrying the point mutation in the region.

LPS induced cytokine production is dependent on MyD88.

LPS can induce functional maturation of MyD88 deficient DCs, including up-regulation of costimulatory molecules and enhancement of APC activity. However, TLR4 deficient splenic CD11c+ DCs can not upregulate their costimulatory molecule expression in response to LPS.

NFkB: In respect to the LPS signaling pathways, NF-kB activation is dependent on TLR4, because it is not obswerved in TLR4 deficient DCs.

However, NF-kB activation is detected at 60 min (delayed induction) after LPS stimulation in MyD88 deficient DCs in a similar level to that observed in wild type DCs.

JNK: LPS induced JNK,activation, which is dependent on TLR4, is detected in MyD88 deficient DCs with delayed kinetcs.

Bacterial DNA 

Maturation: MyD88-urate in response to bacterial DNA, the ligand for TLR9. deficient DCs can not mat