BIOCHEMISTRY - L. Stryer - 1984

VOLUME 3

PART V. MOLECULAR PHYSIOLOGY

CHAPTER 33. IMMUNOGLOBULINS

By the turn of this century, many of the most crucial Properties of the Immune Response had been uncovered. However, METABOLISM/2.html">THE CONCEPT OF defense mechanisms emerged much earlier, as evidenced by Thucydides' account of the plague that struck Athens in 430 BC:

"Let others speculate about its origin and the causes that brought it about, if such a terrible calamity can ever find sufficient explanation... as for me, I shall simply describe its nature and explain the symptoms by which it can be recognized, should it ever break out again. I can do so all the better because I had the disease myself and saw how it progressed in others...

It was precisely upon those who had recovered from the illness that the sick and dying called with particular compassion. Those who had survived knew from personal experience what it was like and no longer feared for themselves, for the same person never fell ill a second time, or at least never died from it. Such people were not only congratulated by others, but in their own joy they were filled with the vain hope that from then on they were safe from any illness whatsoever."

In calling this hope of salvation vain, Thucydides clearly alluded to the Specificity of defense characteristic of The Immune System.

33.1. Basic Definitions

Antibodies (or IMMUNOGLOBULINS) are Proteins synthesized within an animal's body in response to the presence of a foreign substance. An antibody possesses a specific affinity for the foreign substance that stimulated its synthesis. An antigen (or immunogen) is a foreign macromolecule capable of eliciting The production of antibodies. Proteins, Polysaccharides, and Nucleic Acids typically serve as effective Antigens. Antibodies exhibit specificity toward a particular region of the antigen molecule; this region is termed the antigenic determinant.

Small foreign molecules do not elicit the production of antibodies. However, if they are attached to macromolecules, the Synthesis of specific antibodies may occur. In this case, the macromolecule Functions as a carrier for the attached chemical group, referred to as a haptenic determinant. The small foreign molecule itself is called a hapten.

Class="center">Fig. 33.1. Electron micrograph of an antibody molecule crystal

Antibody molecules are secreted by plasma Cells derived from B lymphocytes (Fig. 33.2). Another class of lymphocytes, namely T lymphocytes, mediates the cellular immune response, which complements the humoral response manifested by the appearance of soluble antibodies. In this chapter, we will examine only the humoral response, as its molecular basis is much better understood. It must be emphasized, however, that antibody molecules are merely one component of a large, coordinated system of molecules and cells that recognize and eliminate foreign substances.

Fig. 33.2. Electron micrograph of a B lymphocyte

Fig. 33.3. Electron micrograph of a plasma Cell. A highly developed rough Endoplasmic reticulum is clearly visible