(139) Siglecs in the Porcine Oviduct and Sialylated Ligands on Sperm: Potential Role in the Sperm Reservoir’s Immune Response to Sperm

Leonardo M. Molina¹; Hao-Chun Fan¹; Lauren E. Pepi²; Asif Shajahan²; Parastoo Azadi²; Daniel B. McKim¹; Adrienne M. Antonson¹; David J. Miller¹

1.     Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, United States

2.     Complex Carbohydrate Research Center, University of Georgia, Athens, United State

Abstract Text:

During mammalian insemination, seminal fluid, and sperm elicit myeloid cell infiltration in the uterus, facilitating sperm clearance. However, unlike the uterus, invading sperm do not trigger phagocytic responses in the oviduct in the absence of dysfunction or disease states. Thus, the oviduct possesses a distinct immunological microenvironment that innately tolerates sperm while maintaining the capacity to respond to pathogens. The mechanisms underlying this selective immune tolerance remain poorly understood yet their elucidation could significantly advance the field of reproductive immunophysiology and provide insights into reproductive dysfunction. The sperm glycocalyx has been proposed as a key contributor to innate oviductal tolerance, yet the cell and molecular mechanisms involved remain unclear. The current investigation focused on the role of sialic acid-containing glycoconjugates on sperm and their potential to elicit innate tolerance via cognate sialic acid-binding immunoglobulin-type lectins (Siglecs) expressed in the oviduct. Consistent with this, we identified eight Siglecs expressed in the porcine lower oviduct, five of which are immune inhibitory (Siglecs-2, -3, -5, -10, and -11). Mass spectrometry analysis of porcine sperm revealed the presence of a mixture of α2,3 and α2,6 linked sialic acids with α2,3-linked sialic acids being the predominant linkage type. Of the detected glycans, several sialic acid-containing glycoconjugates were identified as potential ligands for Siglecs, including O-linked glycans: NeuAc1GalNAc1, NeuGc1GalNAc1, NeuAc2Gal1GalNAc1 and glycolipids: NeuAc2Gal1GalNAc1Gal1Glc1, Fuc1Gal1GalNAc1NeuAc1Gal1Glc1. Lectin staining confirmed the location of sialoglycans in the apical region of the sperm head. Spheroids were formed with primary oviduct epithelial cells to model oviduct physiology, enabling the study of the immune response to sperm sialoglycans via qPCR. Results demonstrated that innate sialic acids contribute to sperm immune tolerance, while the addition of α2,6 linked sialic acids triggered an immune response, upregulating IL1β and CXCL8 expression. These findings highlight the broad expression of oviductal inhibitory Siglecs and their potential interactions with sperm sialoglycans. Together, they support a sperm-sialoglycan/oviductal-Siglec axis as a critical component of the oviduct’s unique immunophysiology, essential for undisrupted reproduction in mammals. This research was supported by NIH R24GM137782 to PA, 1R21HD111954-01A1 to DM and AA, and NIH 1F31HD108959 to LM.