Wikipedia
Prostasomes were discovered in 1978 as submicron membranous vesicles (40-500 nm in diameter) secreted by the prostate gland epithelial cells into seminal fluid. They possess an unusual lipid composition and a tight and highly ordered structure of their lipoprotein membranes resembling lipid raft. The physiological role of prostasomes implicates improvement of sperm motility and protection against attacks from the female immune defense during the passage to the egg.
Investigations have shown that cancerous prostate cells and prostate cells with low differentiation continue to produce and secrete prostasomes. The high incidence of prostate cancer in elderly men could take advantage of the immune protective activities supported by the prostasomes.
Immune regulating proteins found in prostasomes include: amino-peptidase N ( CD13); dipeptidyl-peptidase IV ( CD26); enkephalinase (neutral endopeptidase, CD10); angiotensin converting enzyme (ACE, CD143); tissue factor TF ( CD142, thromboplastin); decay accelerating factor ( CD55); protectin ( CD59, inhibitor of MAC) and complement regulatory membrane cofactor protein ( CD46). Prostasomes also contain high levels of the divalent cations: Zn, Ca and Mg.