Ovine/Caprine Interleukin-36 Receptor Antagonist (IL-36Ra) is an anti-inflammatory cytokine that regulates IL-36–mediated immune responses in sheep (Ovis aries) and goats (Capra hircus). The IL-36Ra protein is identical at the amino acid level in these two species, reflecting strong evolutionary conservation of this regulatory cytokine in small ruminants. IL-36Ra is a member of the IL-1 cytokine family and functions as a natural inhibitor of the IL-36 signaling pathway by binding to the IL-36 receptor (IL-36R, also known as IL1RL2) without activating it, thereby preventing proinflammatory cytokines such as IL-36α, IL-36β, and IL-36γ from initiating downstream signaling. Through this mechanism, ovine and caprine IL-36Ra suppress activation of intracellular pathways including NF-κB and MAPK, helping to limit production of inflammatory mediators and regulate immune responses at epithelial barrier tissues such as the skin, respiratory tract, and gastrointestinal mucosa. In sheep and goats, IL-36Ra contributes to maintaining immune homeostasis and controlling excessive inflammatory responses during infection or tissue injury. In cell culture, recombinant ovine/caprine IL-36Ra is commonly used to inhibit IL-36–induced inflammatory signaling in epithelial and immune cells, enabling investigation of cytokine regulation, epithelial–immune cell interactions, and modulation of inflammatory pathways in vitro.