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Isolation Protocol of Mouse Monocyte-derived Dendritic Cells and Their Subsequent In Vitro Activation with Tumor Immune Complexes
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Tumor cells deactivate human monocytes by up-regulating IL-1 receptor associated kinase-M expression via CD44 and

Carlos del Fresno1, Karel Otero, Lourdes Gómez-García

  • 1Research Unit, Department of Surgical Research, La Paz Hospital, Madrid, Spain.

Journal of Immunology (Baltimore, Md. : 1950)
|February 25, 2005
PubMed

Insights

Tumor cells deactivate immune monocytes by increasing IRAK-M expression, a process mediated by hyaluronan via CD44 and TLR4. Restoring monocyte function requires down-regulating IRAK-M, highlighting a new target for cancer immunotherapy.

Area of Science:

  • Immunology
  • Cancer Biology
  • Molecular Medicine

Background:

  • Blood monocytes exhibit anti-tumor activity but are often deactivated in cancer patients.
  • Tumor-associated monocytes show reduced expression of key inflammatory mediators like TNF-alpha and IL-12p40.
  • IRAK-M is known to negatively regulate inflammatory pathways and is upregulated in tolerant monocyte states.

Purpose of the Study:

  • To investigate the role of IRAK-M in the deactivation of human monocytes by tumor cells.
  • To elucidate the molecular mechanisms by which tumor cells induce IRAK-M expression in monocytes.
  • To explore the potential of targeting IRAK-M for restoring monocyte anti-tumor function.

Main Methods:

  • Co-culturing human monocytes with various tumor cell types (live, fixed, and supernatant).
  • Assessing IRAK-M expression at mRNA and protein levels using RT-PCR and Western blotting.
  • Investigating the role of hyaluronan, CD44, and TLR4 using blocking antibodies.
  • Utilizing small interfering RNAs (siRNAs) to down-regulate IRAK-M expression.

Main Results:

  • IRAK-M expression (mRNA and protein) is significantly upregulated in human monocytes cultured with tumor cells.
  • Tumor-derived hyaluronan induces IRAK-M expression via CD44 and TLR4 engagement.
  • Monocytes from leukemia and metastasis patients overexpress IRAK-M.
  • Down-regulation of IRAK-M restores TNF-alpha expression and production in tumor-exposed monocytes.

Conclusions:

  • Tumor cells deactivate human monocytes through the upregulation of IRAK-M.
  • Hyaluronan, acting through CD44 and TLR4, is a key mediator of this IRAK-M induction.
  • Targeting IRAK-M presents a potential strategy to reverse monocyte deactivation and enhance anti-tumor immunity.

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