Surfactant proteins A and D bind CD14 by different mechanisms

Area of Science:

• Immunology
• Pulmonology
• Biochemistry

Background:

• Surfactant proteins A (SP-A) and D (SP-D) are key components of the lung's innate immune system.
• SP-A is known to modulate lipopolysaccharide (LPS)-induced cellular responses via CD14 interaction.

Purpose of the Study:

• To investigate the structural elements of SP-A and SP-D involved in CD14 recognition.
• To understand how these interactions affect the binding of LPS to CD14.

Main Methods:

• Concentration-dependent binding assays of SP-A and SP-D to CD14.
• Inhibition studies using mannose, EDTA, and monoclonal antibodies targeting SP-A domains.
• Analysis of SP-A and SP-D binding to deglycosylated CD14.
• Assessment of SP-A and SP-D effects on CD14 binding to smooth and rough LPS.
• Sucrose density gradient centrifugation to analyze LPS migration.

Main Results:

• Both SP-A and SP-D demonstrated concentration-dependent binding to CD14.
• SP-D binding was inhibited by mannose and EDTA, suggesting carbohydrate recognition.
• SP-A binding was primarily mediated by its neck domain, not the lectin domain, and involved recognition of a peptide component on CD14.
• SP-A bound to deglycosylated CD14, whereas SP-D did not.
• SP-A and SP-D differentially modulated CD14-LPS interactions, with SP-A enhancing rough LPS binding and inhibiting smooth LPS binding.

Conclusions:

• Lung collectins SP-A and SP-D bind to CD14 through distinct mechanisms.
• The SP-A neck domain and SP-D lectin domain are crucial for CD14 binding.
• SP-A interacts with a peptide portion of CD14, while SP-D interacts with a carbohydrate moiety.
• These collectin-CD14 interactions significantly alter the binding dynamics of LPS, impacting innate immune responses in the lung.