Introduction

Abstract

One of the most important survival mechanisms of vertebrates is their ability to recognize and respond to the onslaught of pathogenic microbes to which they are continuously exposed. The collection of host cells and molecules involved in this recognition- response function constitutes its immune system. In man, it comprises about 10¹² cells (lymphocytes) and 10²⁰ molecules (immunoglobulins). Its ontogenic development is constrained by the requirement that it be capable of responding to an almost limitless variety of molecular configurations on foreign substances, while simultaneously remaining inert to those on self components. It has thus evolved to discriminate, with exquisite precision, between molecular patterns.