INTRODUCTION

The immune system of mammals has evolved over millions of years and provides an incredibly elegant protection system which is capable of responding to infective challenges as they arise. The system is fluid-based and both the cells of immunity and their products are transported throughout the body, primarily in the blood and secondarily through fluid within the tissues and organs themselves. All areas of the body are protected by immunity apart from the central nervous system including the brain and eyes. There are several cell types involved in immune responses, each with a role to play and each controlled by chemical mediators known as cytokines. This control is essential as the immune system is such a powerful tool it needs careful management to ensure its effective operation. Both over- and under-activity could have fatal consequences.

All vertebrates have advanced immune systems which show the similarities that you would expect from our common evolutionary past. The more advanced the vertebrate the more complex the immune system. Fish and amphibians have fairly rudimentary immunity with the most sophisticated being found in mammals. The immune system is broadly additive; more complex animals have elements analogous to those found in primitive species but have extra features as well.

For the purposes of this chapter we will focus on the mammalian immune system although the use of birds for antibody production will be discussed in Section 7.1.2.