Lipopolysaccharide induces intracytoplasmic migration of the polymorphonuclear leukocyte CD11b/CD18 receptor

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Integrin receptors like CD11b/CD18 (Mac-1) play crucial roles in immune cell function.
• Lipopolysaccharide (LPS) is a potent immune activator that can modulate cell surface receptor expression.
• Understanding the regulation of CD11b/CD18 is vital for comprehending inflammatory responses.

Purpose of the Study:

• To investigate the impact of LPS on the subcellular localization of the CD11b/CD18 integrin receptor.
• To differentiate between receptor shedding and intracellular transport as mechanisms for LPS-induced changes in CD11b/CD18 expression.
• To elucidate the signaling pathways and cellular components involved in LPS-mediated CD11b/CD18 translocation.

Main Methods:

• Cytoplast preparations to assess cell-associated receptors.
• Subcellular fractionation to determine receptor distribution.
• Inhibition studies using genistein (a protein tyrosine kinase inhibitor).
• Experiments with LPS and human serum, and blocking antibodies against CD14.

Main Results:

• LPS did not alter the total percentage of cell-associated CD11b/CD18 receptors.
• Subcellular fractionation revealed a shift of CD11b/CD18 from the plasma membrane to azurophilic granules upon LPS stimulation.
• Protein tyrosine kinase inhibition blocked this translocation.
• The LPS effect was mimicked by LPS plus serum and blocked by anti-CD14 antibodies, indicating CD14's role.

Conclusions:

• LPS induces intracytoplasmic translocation of CD11b/CD18 receptors to azurophilic granules, rather than shedding.
• This process is dependent on protein tyrosine kinase activation and CD14.
• Endosomal acidification within azurophilic granules may contribute to receptor degradation.