ABSTRACT
The immune system fulfills an essential function in protecting us from the great diversity of infectious agents we encounter in the environment. Although many viruses, bacteria, fungi and protozoa cause “disease”, without a functional immune system the unhindered replication of these organisms usually results in death. Unlike most other organs of the body, the immune system is not a single physical entity. Thus, one of its most complex features is the process by which the various immune cells communicate between themselves and with other tissues of the body. Even the phagocytic cells, that often appear to act independently, are dependent upon signals from other immune and nonimmune cells. In recent years, as we have begun to unravel the many mysteries of the immune system, one of the biggest challenges has been understanding its communication pathways and how they regulate immune processes.
