Immunochemical Recognition and Applications
This issue of Pure and Applied Chemistry (PAC) includes four papers arising from an IUPAC project on immunochemistry that are inter-related insofar as they present descriptions of molecular interactions between molecules of the immune system and their ligands (papers 1 and 2, “Structural aspects of molecular recognition in the immune system, Parts I and II”), and then discuss how a knowledge of this chemistry is furthering the development of both the analytical applications of immune-based sensors (paper 3, “Immunodiagnostics and immunosensor design”), and of better therapies for a variety of human medical conditions (paper 4, “Applications of immunochemistry in human health”). Each paper is structured along the lines of providing some historical context, followed by a critical presentation of our current perspective on the role chemistry is playing in the basic understanding of the immune system and its potential for exploitation. The intricacies of the human immune system represent one of the most complex areas of current biology; indeed, in a forum in Scientific American (April 2012), Stuart Firestein noted that, as a neurobiologist, he can “understand the questions that drive immunology”, but though he “can’t grasp much of immunology ... the wonderful thing is that most immunologists can’t either”. The point was, of course, the increasing specialization of all fields of science, but the example was well chosen. And so, as a group of chemists, physicians, and biologists, the authors are nevertheless challenged to put the field into a comprehensible narrative for the members of IUPAC and the readers of PAC. Hopefully, we have met this challenge, in part by including information boxes in the first two papers that are intended as a minimal introduction to the immune system. The immune system handles the body’s reaction to invading microbes, allergens, and other foreign substances. It has two subsystems. The first, called “acquired” (or “adaptive”), recognizes non-self-structures of the invader and counteracts them with molecular responses that reflect a memory of previous exposure. This is what happens when, for example, we are vaccinated, become immune to recurrent disease, or develop allergies; it relies upon antibodies – immunoglobulin proteins – produced by “B cells” and upon surface receptor proteins on “T cells”. The second subsystem of immunity, described as “innate”, recognizes and then counteracts microorganisms and/or viruses based on certain specific chemical structures that do not occur in vertebrates. This involves molecules with arcane names like NOD, Toll-like, and RIG-like helicase receptors. Both subsystems of immunity involve intricate processes of molecular recognition. In the first two papers, we present a number of crystal structures to demonstrate how the recognition process occurs at a structural level, and also to illustrate the beauty of the common themes and subtle variations of these interactions. We have chosen examples that reflect current interest in research, recognizing that the focus of much of this research is on infectious and autoimmune diseases.