Expression of Interleukin-1 System Genes in Human Gametes

There is considerable evidence that the interleukin-1 (IL-1) system plays an important role in ovarian and testicular physiology, implantation, and other reproductive events. Human embryos express IL-1β, IL-1 receptor type I (IL-1RtI), and IL-1 receptor antagonist (IL-1RA) at both the mRNA and protein levels. The presence of IL-1α and IL-1β in oocyte-conditioned media and on the surface of human oocytes suggests that these cells may also produce this cytokine; however, whether the IL-1 system gene products are present as stable mRNAs in human gametes (oocytes and spermatozoa) has not yet been demonstrated. We used stringent cell separation techniques combined with reverse transcription-polymerase chain reaction to investigate the expression of various IL-1 system genes (IL-1α, IL-1β, IL-1RtI, and IL-1RA) in human gametes and cumulus cells. Our results indicate that freshly isolated cumulus cells express all these IL-1 system components. On the other hand, IL-1α, IL-1β, and IL-1RtI mRNAs were not found in either unfertilized or fertilized human oocytes, and a very few metaphase II human oocytes had transcripts for either secreted (10%) or intracellular (17%) IL-1RA. Mature spermatozoa did not contain mRNA for any of the of the IL-1 system components. The absence of informational RNA for the IL-1 system components in human unfertilized and polyploid oocytes and fresh immature oocytes suggests that maternal transcripts for these genes do not contribute to early embryo development. The presence of IL-1 components at the protein level in human oocytes may be due to binding of IL-1 produced by cumulus cells or other cell types, or to prior intrafollicle transcription and translation. Likewise, IL-1 system components do not appear to have a physiological role in mature spermatozoa since none of these components are present at the mRNA or protein levels, and important functional parameters such as motility and acrosome reaction appear not to be affected by IL-1β in vitro. However, the abundant expression of IL-1α, IL-1β, the IL-1RtI, and its antagonist IL-1RA by human cumulus cells provides further evidence that the IL-1 system plays a role in human ovarian physiology.