Aims

To introduce the reader to:

• the concept of immunity against bacterial infections

• the cell populations involved

• the soluble mediators involved

• the organisation of the immune system

• innate immunity and recognition of pathogens

• mechanisms of phagocytosis and bacterial killing: linking innate and acquired immunity

• acquired immunity, generation of diversity and antigen presentation

• how these systems work together to kill bacteria

Introduction

Many of our defence mechanisms against infection function at mucosal surfaces, are continually active and are generally invisible to us. These various defence systems have been described in Chapter 5 and the linkage between epithelial ‘immunity’ and what would classically be called immunity has been made. This chapter will consider the antibacterial defence mechanisms that can be thought of as being ‘post-mucosal’ and will describe the systems of cells and mediators that are normally thought of when the term ‘immunity’ is used. The reader has to understand that, for the purposes of teaching, the various systems that defend us against bacterial infection are parcelled up into distinct categories (‘innate’ versus ‘acquired’, or ‘humoral’ versus ‘cellular’). However, in reality, they work as one seamless mechanism. Unfortunately, we do not yet understand all the links that exist between these systems and the challenge is to identify the connections.

Before entering the fascinating realm of antibacterial immunity, the reader must be warned that modern immunology, which has developed largely since the 1960s, was created at a period when the world thought itself safe from bacterial infections.