Exploiting escherichia coli–sperm interactions to identify sperm antigen for the development of an immunocontraceptive

The unprecedented rise in global population has intensified the need for safe, effective, and reversible contraceptive strategies to mitigate the far-reaching consequences of overpopulation. In recent decades, immunocontraception has emerged as a promising and biologically rational approach targeting gamete production, gamete outcome, or gamete function. Amongst these, use of sperm antigens (gamete function) seems to be an exciting and alternative approach for the development of contraceptive vaccines (CVs). However, the use of whole spermatozoa or crude sperm extracts is impractical, as they contain multiple antigens shared with somatic cells, risking autoimmune responses through molecular mimicry. The contraceptive utility of an antigen is contingent upon its immunogenicity, expression on sperm surface and involvement in fertility/fertilization. Therefore, identification and characterization of sperm-specific antigens (SSAs) is crucial for developing targeted, sperm-selective CVs. To delineate SSAs, several cutting-edge approaches; genomics, proteomics, recombinant DNA technology, hybridoma development, and gene knockout studies are currently being employed in different laboratories worldwide. However, an innovative and relatively unexplored strategy involves investigating the interactions between bacteria and spermatozoa, which often mimic antigen–antibody type binding. Certain microorganisms viz Escherichia coli, Staphylococcus aureus, Ureaplasma urealyticum, and Mycoplasma hominis, are known to adhere to and agglutinate spermatozoa, thereby impairing motility and fertility. These interactions use specific host cell-surface molecules known as receptors and such receptors provide a mechanism for interaction with ligand on bacteria. The present study reported the isolation and purification of ligand i.e. sperm agglutinating factor (SAF) from E. coli that could induce sperm agglutination, death, and morphological changes in human spermatozoa in-vitro along with infertility in female BALB/c mice. Fluorescent microscopy revealed the binding of FITC tagged SAF over entire surface of spermatozoa postulating that a receptor mechanism might be involved in SAF-sperm interaction resulting in SAF induced impairment. Hence, using SAF as a tool, corresponding sperm receptor (SR) from spermatozoa was extracted, purified and characterized. Further, an attempt was made to generate anti-SR antibodies to evaluate the immunocontraceptive potential. Anti-SR polyclonal antibodies were generated by immunizing BALB/c mice with SR. In-vitro assays demonstrated that anti-SR antibodies impaired sperm motility via agglutination, induced sperm death, and caused morphological abnormalities. The induction of sperm damage was specifically due to anti-SR polyclonal antibodies as it could be mitigated by addition of purified SR depicted by competitive inhibition assays. For in-vivo validation, when a single dose of anti-SR serum was administered intravaginally in female BALB/c mice, complete inhibition of conception was observed in contrast to mice receiving pre-immune serum or PBS. Also, simultaneous administration of purified SR antigen could restore fertility. Histopathological examination of reproductive tissues (ovary, uterus, vaginal epithelium) revealed no signs of inflammation, tissue damage, or immune cell infiltration, confirming non-toxic and sperm-specific nature of elicited immune response. The present study highlighted that the interaction between sperm-E. coli can be exploited to isolate the antigen on human spermatozoa that may serve as a potential candidate for the development of contraceptive vaccines, acting as targets for both passive and active immunization strategies.

Dr. (Mrs.) Vijay Prabha did her B.Sc. (Hons),  M.Sc. (Hons), and Ph.D. from the Department of Microbiology, Panjab University, Chandigarh, India. She joined the same department as Assistant Professor and then obtained the position of Associate Professor and Professor. She has 32 years of teaching and 42 years of research experience. She has published 111 research articles in reputed journals. She has presented her work in various national and international conferences as an invited speaker and keynote speaker. She is member of various Biosafety committees and learned societies. She is Editorial Board member of various national and international journals.