**8. Innate and adaptive immunity in xenotransplantation**

The immune system has two inter-related arms; the innate and the adaptive immune systems, both of which contribute to the rejection of xenotransplanted cells, tissues and organs. Although often described as separate, the systems have a large network of connections which are interdependent, and thus are not completely distinct. Both systems utilize multiple mechanisms to protect the host, creating a series of defense layers of increasing specificity. When functioning properly, a given layer may not be 100% efficient, but in aggregate will capture the overwhelming majority of pathogens. In addition, the ability to detect subtle differences between highly related cells has the potential benefit of identifying and eliminating cells with oncogenic mutations, preventing tumors before they have a chance to establish themselves [21].
