Ingested soluble CD14 contributes to the functional pool of circulating sCD14 in mice

Area of Science:

• Immunology
• Neonatal Nutrition
• Molecular Biology

Background:

• Soluble CD14 (sCD14) is a key immune co-receptor found in human milk and bodily fluids.
• sCD14 recognizes bacterial lipopolysaccharide (LPS) via Toll-like receptor 4 (TLR4), initiating immune responses.
• Previous studies suggested gastrointestinal transfer of ingested sCD14 in neonatal rats, but its contribution to infant circulation and functionality remained unclear.

Purpose of the Study:

• To determine if human milk sCD14 contributes to circulating sCD14 levels in infants.
• To assess the functionality of ingested sCD14 in the infant bloodstream.
• To investigate the role of TLR4 in the intestinal transfer of sCD14.

Main Methods:

• Utilized CD14-deficient (CD14-/-) mouse pups fostered to wild-type (WT) mothers producing sCD14 in milk.
• Measured circulating sCD14 levels in fostered pups via ELISA.
• Assessed immune response (IL-6, TNF-α) to LPS in CD14-/- pups.
• Investigated sCD14 transcytosis across Caco-2 intestinal cells with TLR4 knockdown.

Main Results:

• Ingestion of sCD14 led to detectable blood levels (0.16±0.09μg/mL) in CD14-/- pups, representing a significant portion of WT levels.
• Ingested sCD14 remained functional, significantly increasing IL-6 and TNF-α production in response to LPS.
• TLR4 knockdown significantly reduced sCD14 transcytosis in Caco-2 cells, indicating TLR4's involvement in transfer.

Conclusions:

• Human milk sCD14 is bioavailable and contributes to infant systemic circulation.
• Ingested sCD14 retains its immune-modulating functionality in the infant.
• The transfer of sCD14 across the infant gut likely involves TLR4, underscoring the importance of breast milk's immune components and the inadequacy of current infant formulas.