Seminal plasma protects frozen-thawed ram spermatozoa from neutrophil attack: a complement mediated dynamic

Area of Science:

• Reproductive immunology
• Animal reproduction
• Immunology

Background:

• Frozen-thawed ram spermatozoa exhibit reduced fertility post-insemination.
• This decline is linked to an increased immune response in the ewe's cervix.
• Seminal plasma (SP) is known to aid sperm transport, but its protective components are unidentified.

Purpose of the Study:

• To investigate the immune interactions between frozen-thawed ram spermatozoa and polymorphonuclear neutrophils (PMNs).
• To determine the immunoprotective effect of ram seminal plasma (SP) against sperm-PMN binding.
• To identify the nature of the heat-labile factor in SP responsible for this protection.

Main Methods:

• Utilized a neutrophil binding assay to quantify sperm-PMN interactions.
• Compared binding in frozen-thawed (FT) sperm with and without 25% SP supplementation.
• Investigated the role of heat-labile factors by comparing native SP with heat-treated SP (HTSP).

Main Results:

• SP significantly reduced sperm-PMN binding compared to FT sperm alone.
• Heat-treated SP (HTSP) showed similar binding susceptibility to FT sperm, indicating a heat-labile protective factor in SP.
• Ewe serum increased sperm-neutrophil binding, an effect mitigated by heat-treatment, suggesting serum proteins (like complement) also play a role.

Conclusions:

• Ram seminal plasma possesses significant immunoprotective properties against neutrophil binding to spermatozoa.
• The protective effect is attributed to heat-labile components within the seminal plasma.
• These findings suggest SP can be utilized to improve the fertility of frozen-thawed ram sperm by mitigating immune responses during cervical transit.