Egress of sperm autoantigen from seminiferous tubules maintains systemic tolerance (Mar 2017)

Egress of sperm autoantigen from seminiferous tubules maintains systemic tolerance
J Clin Invest. 2017 Mar 1;127(3):1046-1060
Tung KS, Harakal J, Qiao H, Rival C, Li JC, Paul AG, Wheeler K, Pramoonjago P, Grafer CM, Sun W, Sampson RD, Wong EW, Reddi PP, Deshmukh US, Hardy DM, Tang H, Cheng CY, Goldberg E.
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Short description:
Autoimmune responses to meiotic germ cell antigens (MGCA) expressed in the testis and on sperm are detected in 3%–12% of men with spontaneous infertility, which is a factor in 5% of couples desiring children (1). Testes biopsies have revealed that 50% of the patients had focal orchitis (2). Of the 0.5 million men in the USA who choose vasectomy as a contraceptive approach each year, 70% develop sperm Ab responses with undefined long-term sequelae. In addition, MGCA are expressed as cancer/testis antigens (CTA) in many human epithelial tumors, melanomas, and leukemias. They are targets of tumor immunity and cancer vaccine candidates (3, 4). A better understanding of these tissue-specific and cancer-specific antigens in human diseases will require fuller knowledge of the sequestration and tolerance statuses of MGCA in normal and pathological states. Surprisingly, there have been little or no research efforts to address these critical issues.
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Abstract taken from PubMed

Autoimmune responses to meiotic germ cell antigens (MGCA) that are expressed on sperm and testis occur in human infertility and after vasectomy. Many MGCA are also expressed as cancer/testis antigens (CTA) in human cancers, but the tolerance status of MGCA has not been investigated. MGCA are considered to be uniformly immunogenic and nontolerogenic, and the prevailing view posits that MGCA are sequestered behind the Sertoli cell barrier in seminiferous tubules. Here, we have shown that only some murine MGCA are sequestered. Nonsequestered MCGA (NS-MGCA) egressed from normal tubules, as evidenced by their ability to interact with systemically injected antibodies and form localized immune complexes outside the Sertoli cell barrier. NS-MGCA derived from cell fragments that were discarded by spermatids during spermiation. They egressed as cargo in residual bodies and maintained Treg-dependent physiological tolerance. In contrast, sequestered MGCA (S-MGCA) were undetectable in residual bodies and were nontolerogenic. Unlike postvasectomy autoantibodies, which have been shown to mainly target S-MGCA, autoantibodies produced by normal mice with transient Treg depletion that developed autoimmune orchitis exclusively targeted NS-MGCA. We conclude that spermiation, a physiological checkpoint in spermatogenesis, determines the egress and tolerogenicity of MGCA. Our findings will affect target antigen selection in testis and sperm autoimmunity and the immune responses to CTA in male cancer patients.
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