Defensins are small proteins that play a crucial role in the immune system. They are produced by various cells in the body, including white blood cells and epithelial cells, and help protect against infections by disrupting the membranes of bacteria, fungi, and some viruses. These proteins are categorized into three main types: alpha-defensins, beta-defensins, and theta-defensins, each with unique structures and functions. Defensins not only have antimicrobial properties but also contribute to the regulation of inflammation and the recruitment of immune cells to sites of infection.