Anti-SPACA5B antibodies are used in the immunodetection of the protein sperm acrosome associated 5B. It is notably expressed in the testis. Synonyms for this target antigen include SLLP-X, lysozyme-like protein 5, sperm-specific lysozyme-like protein X, and sperm acrosome-associated protein 5. SPACA5B gene orthologs have been reported in the rat species.