Boundaries of Immune Reactivity: Implications for the Relationship of Man to His Environment

Abstract

It is a phenomenon characteristic of the mammalian immune system that immunoglobulins can be produced that recognize foreign organisms. This characteristic is important in thwarting pathological infestations, but the implications of the potential recognition of diverse elements in the human ecosystem extend further. Immunoglobulins do not recognize everything. There are boundaries to their potential repertoire that define the sphere of immune reactivity. To consider that sphere is to explore the edges of the immune system—an exploration that is, I believe, interesting and informative. Immunoglobulins can bind to multicellular parasites, eukaryotic amoebas, fungi, bacteria, and viruses; but this list does not really describe the range of immune reactivity since immunoglobulins bind to molecular structures on these organisms and not to the whole organisms. What molecular structures are recognized? Immunoglobulins can bind to protein macromolecules, to nucleic acid macromolecules, and to sugar macromolecules. It is important to note that they cannot recognize amino acids, nucleic acids, or simple sugars by themselves but instead require interaction with larger determinants. It was demonstrated in a series of experiments with proteins and sugars containing increasing numbers ofsubunits that immunoglobulins can recognize as few as three of these subunits combined in a chain but not less [I]. It appears that immunoglobulins can bind to determinants with molecular weights greater than 250 daltons or with dimensions in the range of tens to Supported in part by PHS grants A122505 and CA36189 awarded by the NIH and by a Hartford Foundation fellowship. The author thanks Drs. K. Smachlo and M. Lamm for their helpful suggestions and Ms. J. Nagy for secretarial assistance. This essay received honorable mention in the 1986 Dwight J. Ingle Memorial Writing Award for authors under 36.