Lipopolysaccharide-binding protein is produced in the epididymis and associated with spermatozoa and prostasomes

Area of Science:

• Reproductive immunology
• Innate immunity
• Human reproductive biology

Background:

• Lipopolysaccharide-binding protein (LBP) is a key acute phase protein in host defense against Gram-negative bacteria.
• LBP binds bacterial lipopolysaccharides, initiating signaling via CD14 and Toll-like receptor (TLR)-4, crucial for inflammatory responses.

Purpose of the Study:

• To investigate the presence and potential role of lipopolysaccharide-binding protein (LBP) in the human reproductive system.
• To determine if LBP is expressed in the epididymis and seminal fluid and if it interacts with spermatozoa or prostasomes.

Main Methods:

• In situ hybridization to detect LBP gene expression in the human epididymis.
• Immunohistochemistry to localize LBP protein in epididymal epithelium and spermatozoa.
• Western blot analysis of seminal plasma, spermatozoa, and prostasomes for LBP.
• Gel filtration to assess LBP colocalization with prostasomes.
• Quantification of LBP concentration in seminal plasma.

Main Results:

• Constitutive expression of the LBP gene was observed in the human epididymis epithelium.
• LBP protein was detected in epididymal cells and attached to spermatozoa (heads and tails).
• Western blot confirmed LBP presence in seminal plasma, spermatozoa, and prostasomes.
• Gel filtration indicated that LBP colocalizes with prostasomes.
• The mean concentration of LBP in seminal plasma was determined to be 127+/-42 ng/mL.

Conclusions:

• Lipopolysaccharide-binding protein (LBP) is constitutively expressed in the human epididymis and present in seminal plasma.
• LBP associates with spermatozoa and prostasomes, suggesting potential roles in human reproduction.
• These findings highlight a previously unrecognized function of LBP beyond bacterial defense, extending into reproductive immunology.