Evolution of CD33-related siglecs: regulating host immune functions and escaping pathogen exploitation?

Area of Science:

• Immunology
• Evolutionary Biology
• Glycobiology

Background:

• Siglecs are immune receptors binding sialylated glycans, crucial for cell signaling.
• CD33-related Siglecs (CD33rSiglecs) expanded in mammals via gene duplication, with humans having more than rodents.
• Most CD33rSiglecs are inhibitory, but activating variants like siglec-14 and siglec-16 exist.

Purpose of the Study:

• To explore the evolutionary expansion and functional diversity of CD33rSiglecs.
• To understand the roles of inhibitory and activating Siglecs in immune regulation.
• To investigate pathogen exploitation of Siglecs in host defense.

Main Methods:

• Comparative genomics to analyze CD33rSiglec gene evolution across mammals.
• Functional assays to characterize inhibitory and activating Siglec signaling pathways.
• Studies on pathogen-Siglec interactions, including bacterial binding and immune suppression.

Main Results:

• CD33rSiglec gene family expanded significantly in mammals, with rodents showing gene loss compared to humans.
• Activating CD33rSiglecs (e.g., siglec-14, siglec-16) paired with inhibitory receptors provide alternative immune signaling pathways.
• Inhibitory Siglecs regulate innate immunity (TLR signaling) and adaptive immunity (B1-cell expansion, inflammation).
• Pathogens like Group B Streptococcus exploit Siglec-9 on neutrophils to evade host killing.

Conclusions:

• The evolution of CD33rSiglecs, including activating variants, offers enhanced host defense mechanisms against pathogens.
• Siglecs play critical roles in modulating immune responses, from innate pathogen recognition to adaptive immune cell regulation.
• Pathogen strategies to exploit Siglecs highlight their importance in host-pathogen interactions and immune evasion.