CD33/Siglec-3 binding specificity, expression pattern, and consequences of gene deletion in mice

Area of Science:

• Immunology
• Molecular Biology
• Glycobiology

Background:

• Mouse CD33/Siglec-3 (mCD33) is the apparent ortholog of human CD33/Siglec-3 (hCD33), a Siglec family member involved in immune regulation.
• Understanding mCD33's specificities and functions is crucial for comparative immunology and potential therapeutic targeting.

Purpose of the Study:

• To characterize the binding specificity and expression pattern of mCD33.
• To investigate the in vivo functions of mCD33 by generating and analyzing knockout mice.

Main Methods:

• Generation of mCD33-deficient mice.
• Analysis of mCD33 expression on myeloid cells.
• Assessment of mCD33 binding to various sialic acid structures, including mucins and sialyl-Tn.
• Evaluation of knockout mouse phenotype, leukocyte subpopulations, and inflammatory responses.

Main Results:

• mCD33 is primarily expressed on mature granulocytes in peripheral blood, unlike hCD33.
• mCD33 exhibits unique sialic acid-dependent binding to mucin glycans and the sialyl-Tn epitope, differing from hCD33's binding profile.
• mCD33-deficient mice are viable and fertile with no significant morphological, histological, or leukocyte subpopulation abnormalities.
• Inflammatory responses and IL-6 secretion were largely unaffected in mCD33 knockout mice.

Conclusions:

• There are substantial species-specific differences in CD33 expression and ligand recognition between mice and humans.
• The lack of a significant phenotype in mCD33-deficient mice suggests functional redundancy with other myeloid Siglec proteins.