Choosing between immunity and tolerance after transplantation.

Transplantation of MHC disparate solid organ leads to activation of both innate and adaptive immune responses. These immune responses include both effector and regulatory limbs. Lymphodepletion and IL-2 blockade may control the acute alloimmune response in humans but may also limit the regulatory arm. Numerous cytokines involved in rejection appear to be critical for tolerance. TLRs,complement engagement can facilitate suppressive responses as well as effector responses. Facilitating antigen-specific tolerance while enabling robust immunity may require ex vivo manipulation of the immune system rather than relying on in vivo perturbations of the homeostatic process.