Aims

The main aims of this chapter are to introduce the reader to:

• the concept of signalling in biology

• the role of intracellular signalling in normal eukaiyotic cell control

• eukaryotic intracellular signalling mechanisms

• cell–cell signalling in eukaiyotes

• the role of cytokines as cell–cell signalling controllers

• prokaryotic intracellular signalling

• prokaryotic cell–cell signalling

• prokaryote–eukaryote cell signalling

• the concept that bacteria manipulate eukaryotic signalling mechanisms to induce pathology

Introduction

Communication – the transfer of information – is part of our everyday lives and we are all participants in a rapidly expanding planet-wide communication experiment. It is also obvious that animals communicate – by using smell, sound and visual cues. The dawn chorus is a good example of animals signalling to each other. However, it may be less apparent that the maintenance of a multicellular organism is absolutely dependent on the correct transmission and reception of signals. To maintain the mammalian body in a healthy state requires an enormous number of signals. There are three major signalling systems in multicellular organisms and these are classified as neural, endocrine and cytokine. These individual systems also interact with each other in ways that are only now becoming apparent.

One way of looking at disease is as a disturbance in the signalling that generates the dynamically stable state known as homeostasis. This term defines the optimal conditions of the multitude of body systems required for normal functioning. Disturbances of endocrine hormone secretion, for example, are well-known causes of disease.