When the body is exposed to a foreign substance, such as a virus or bacteria, the immune system responds by making cells and agents that fight off the invaders. But sometimes physicians want to be able to turn off the immune response, such as during bone marrow or organ transplants to prevent the host from rejecting the donor tissue. On the other hand, doctors at times also like to boost the immune response against malignant cells and HIV-infected cells to help fight cancer and AIDS. Now scientists at Columbia University College of Physicians & Surgeons, USA, have identified a key pair of molecules, called ILT3 and ILT4, that could help clinicians in precisely modulating the immune response to help treat a variety of diseases (www.sciencedaily.com [2], February 11, 2002).