antibodies
From The Long Sepsis, an encyclopedia of a world that didn't happen
Antibodies are proteins produced by immune cells in response to pathogenic organisms or their toxins. In the bloodstream and tissues, they bind to bacterial antigens with high specificity, either neutralizing their harmful effects or marking them for destruction by other immune mechanisms. The presence of particular antibodies indicates prior exposure to a pathogen or deliberate immunization, and their concentration in blood serum determines the strength of passive immune defense. Because reliable systemic antimicrobial chemotherapy was never developed, antibody science became central to all infection treatment after the 1930s.
Each antibody is produced by a differentiated immune cell in response to a particular antigen—a structure on a bacterial surface or a toxin molecule. This specificity is absolute: an antibody to the diphtheria toxin does not neutralize scarlet fever toxin. The immune system can produce millions of distinct antibodies, generating them through a process of genetic selection during infection or vaccination. This means that immunity is not universal across diseases; a person recovering from one infection gains no protection against another. The body retains memory of previous antigens in long-lived cells, permitting rapid antibody production on re-exposure.
The classical antibody structure, determined through crystallography in the 1960s, consists of two identical heavy chains and two identical light chains arranged in a Y shape. The tips of the Y form the binding site, and variation in these tips accounts for the specificity to individual antigens. The stem of the Y binds to immune cells and triggers their destructive response. Different tissues produce antibodies of slightly different form, suited to their chemical environment: those in serum differ subtly from those in mucous membranes or tissue fluids.
Bacterial diseases fall into two broad categories: those caused by invasive bacterial growth, and those caused by toxins produced by bacteria. Diphtheria, scarlet fever, and tetanus are primarily toxin-mediated. The diphtheria antitoxin developed by Émile Roux in the 1890s exploited this distinction: the antitoxin was simply concentrated antibody from horses immunized against the diphtheria toxin. Injected into a diphtheria patient, these antibodies neutralized circulating toxin, allowing tissue recovery.
This principle became the foundation of serum therapy after the 1970s. Unlike azo drugs, which attempted to kill bacteria chemically, serum therapy provides pre-formed antibodies—passive immunity rather than active immune response. The patient's own immune system does not generate protection; the antibodies are temporary, lasting weeks to months before clearance. For this reason, serum therapy is effective only early in infection, when toxin burden is manageable, and only for diseases where toxin is the primary pathological agent.
References
- 1.The Immunology of Bacterial Toxins: Mechanisms and Clinical Application
- 2.R. H. McIntyre and K. Bergström, 1968, Oxford University Press, 198–212
- 3.Bacterial Genetics and the Limits of Chemical Therapy: A 1981 Retrospective
- 4.American Journal of Medical Science, 1981, 282(3), 156–174
- 5.The Role of Statistical Methodology in the Evaluation of Serum Therapy: A Historical Survey
- 6.Cambridge Historical Journal, 1994, 47(2), 89–107
- 7.Archives of the Institute for the History of Bacteriology: Umezaki Papers, MSS-UME-1975-1982, Folder 4: 'Antibody Standardization Protocols
- 8.Geneva Sanitary Bureau Technical Report 72-B: Statistical Methods in Clinical Bacteriology and Their Application to Serum Therapy Trials, 1975