Ingested soluble CD14 contributes to the functional pool of circulating sCD14 in mice.
Soluble CD14 (sCD14) is a pattern recognition receptor and Toll-like co-receptor observed in human milk (5-26μg/mL) and other bodily fluids such as blood (3μg/mL). The most well defined role of sCD14 is to recognize lipopolysaccharide of Gram-negative bacteria and signal an immune response through Toll-like receptor 4 (TLR4). Previous research has shown ingested sCD14 to transfer from the gastrointestinal tract and into the blood stream in neonatal rats. The contribution of human milk sCD14 to circulating levels in the infant and the functionality of the protein, however, remained unknown. Using CD14(-/-) mouse pups fostered to wild type (WT) mothers expressing sCD14 in their milk, we show herein that ingestion of sCD14 resulted in blood sCD14 levels up 0.16±0.09μg/mL. This represents almost one-third (26.7%) of the circulating sCD14 observed in WT pups fostered to WT mothers (0.60±0.14μg/mL). We also demonstrate that ingested-sCD14 transferred to the blood remains functional in its ability to recognize lipopolysaccharide as demonstrated by a significant increase in immune response (IL-6 and TNF-α) in CD14(-/-) pups fostered to WT mothers in comparison to control animals (P=0.002 and P=0.007, respectively). Using human intestinal cells (Caco-2), we also observed a significant decrease in sCD14 transcytosis when TLR4 was knocked down (P<0.001), suggesting sCD14 transfer involves TLR4. The bioavailability of human milk sCD14 established in this report confirms the importance of human milk proteins for the infant and demonstrates the need to improve infant formulas which are lacking in immune proteins such as sCD14.
Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada.
Tonya L
TL
Ward
Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada.
Kagami
K
Goto
Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada. Electronic address: altosaar@uottawa.ca.
Illimar
I
Altosaar
D000818:Animals; D000831:Animals, Newborn; D000833:Animals, Suckling; D018938:Caco-2 Cells; D005247:Feeding Behavior; D015870:Gene Expression / Q000276:immunology; D019073:HT29 Cells; D006801:Humans; D015850:Interleukin-6 / Q000097:blood / Q000276:immunology; D007774:Lactation / Q000235:genetics / Q000276:immunology*; D018950:Lipopolysaccharide Receptors / Q000097:blood* / Q000235:genetics / Q000276:immunology*; D008070:Lipopolysaccharides / Q000276:immunology; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D008892:Milk / Q000276:immunology*; D021381:Protein Transport / Q000276:immunology; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000097:blood / Q000276:immunology
D015850:Interleukin-6; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha
CD14; Human milk; Infant; Necrotizing enterocolitis; TLR4; Transcytosis; sCD14