Expression of Bisecting Type and Lewisx/Lewisy Terminated N-Glycans on Human Sperm

Abstract

Human sperm lack major histocompatibility class I molecules, making them susceptible to lysis by natural killer (NK) cells. Major histocompatibility class I negative tumor cells block NK cell lysis by expressing sufficient amounts of bisecting type N-glycans on their surfaces. Therefore, sperm could employ the same strategy to evade NK cell lysis. The total N-glycans derived from sperm were sequenced using ultrasensitive mass spectrometric and conventional approaches. Three major classes of N-glycans were detected, (i) high mannose, (ii) biantennary bisecting type, and (iii) biantennary, triantennary, and tetraantennary oligosaccharides terminated with Lewis x and Lewis y sequences. Immunostaining of normal sperm showed that glycoproteins bearing Lewis y sequences are localized to the acrosome and not the plasma membrane. In contrast, defective sperm showed distinct surface labeling with antiLewis y antibody. The substantial expression of high mannose and complex type N-glycans terminated with Lewis x and Lewis y sequences suggests that sperm glycoproteins are highly decorated with ligands for DC-SIGN. Based on previous studies, the addition of such carbohydrate signals should inhibit antigenspecific responses directed against sperm glycoproteins in both the male and female reproductive systems. Thus, the major N-glycans of human sperm are associated with the inhibition of both innate and adaptive immune responses. These results provide more support for the eutherian fetoembryonic defense system hypothesis that links the expression of carbohydrate functional groups to the protection of gametes and the developing human in utero. This study also highlights the usefulness of glycomic profiling for revealing potential physiological functions of glycans expressed in specific cell types.Studies performed over the past four decades indicate that conditions are not optimal for human sperm in the female reproductive system (1). Women release neutrophils, monocytes, and lymphocytes from the specialized mucosal surface of their cervix during the leukocyte reaction after coitus (2, 3). This sequestration occurs specifically in response to contact with sperm but not seminal plasma (2, 3). Increased immunological awareness related to histocompatibility and its implications for reproduction in eutherians initially raised concerns about how foreign human sperm are tolerated in the female reproductive system (4). Early studies suggested that human sperm express MHC 3 class I molecules that define self, suggesting the possibility that histocompatibility based responses must be suppressed in the female reproductive tract (5). However, more recent studies confirm that sperm precursors down-modulate their MHC class I molecules, yielding mature sperm that are MHC class I negative cells (5). This absence enables these gametes to evade histocompatibility based responses mediated by MHC class I-restricted cytotoxic T lymphocytes (6).This lack of MHC class I molecules does not make sperm completely invulnerable to cell mediated responses...

Tumor Biomarker Glycoproteins in the Seminal Plasma of Healthy Human Males Are Endogenous Ligands for DC-SIGN

“…Free oligosaccharides capped with these sequences were also present in human seminal plasma (16). More recent ultrasensitive mass spectrometric analyses have confirmed the prolific expression of N-glycans bearing antennae terminated with multiple Lewis x and Lewis y epitopes on glycoproteins associated with human sperm and seminal plasma (17,18). These observations indicated that there could be many endogenous glycoprotein ligands for DC-SIGN in the male reproductive system.…”

Analysis of carbohydrates and glycoconjugates by matrix‐assisted laser desorption/ionization mass spectrometry: An update for 2007–2008

“…Highly fucosylated complex glycans have been characterized in human sperm as per-methylated products by MALDI-TOF/TOF and combined gas chromatography/ mass spectrometry (GC/MS). Tetra-antennary glycans with up to nine attached fucose residues (48) were identified (Pang et al, 2007).…”

Characterization of Helicobacter pylori α1,2‐Fucosyltransferase for Enzymatic Synthesis of Tumor‐Associated Antigens

“…[1] They serve as the determinants of human blood groups and mediate cell-cell interactions that trigger several important biological events such as fertilization, [2] embryogenesis, [3] neuronal development, [4] and immune response. On the other hand, it has been shown that fucose-containing carbohydrate structures displayed on the cell surface are also associated with the emergence and progression of chronic inflammation and cancer.…”