The humoral immune system is a part of the immune system which defends the body against invading organisms and other foreign material.
The humeral part is done by macromolecules outside the cells. These may be secreted antibodies, complement proteins, or certain antimicrobial peptides. Their job is to attack bacteria (and other foreign substances) which are loose in the blood stream or other fluids. In older medicine, these fluids were called "humors". Both the more primitive innate immune system, and the later acquired or adaptive immune system of vertebrates, have humoral components.
The humoral immune system contrasts with the cell-mediated immunity. That involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
How the humoral system worksEdit
The main cells that make it work are the B cells, which create and secrete antibodies that seek out the invaders and attach to them. Once the invader is coated in antibodies, this targets the invader for destruction by other parts of the immune system. Before the B cell can create antibodies, it first needs T helper cells to 'teach' the B cell about details of the incoming invader. This is a key part of the adaptive immune system, and the reference attached here summarizes the process.
The production of antibodies tailor-made to combat particular bacteria is the most important element, but there are a number of other humeral defenses from the more primitive innate immune system.
|Soluble components in the serum
that are capable of killing microorganisms
Ehrlich (1892) 
|Antitoxins||Substances in the serum that can neutralize
the activity of toxins. This is passive immunization
|von Behring and Kitasato (1890)|
|Bacteriolysins||Serum substances that work with the
complement proteins to induce bacterial lysis
|Richard Pfeiffer (1895)|
|Serum substances that agglutinate bacteria
and precipitate bacterial toxins
|von Gruber and Durham (1896),|
|Haemolysins||Serum substances that work with complement
to lyse red blood cells
|Belfanti and Carbone (1898) |
Jules Bordet (1899)
|Opsonins||Serum substances that coat the outer membrane
of foreign substances and enhance the rate of
phagocytosis by macrophages
|Wright and Douglas (1903)|
|Antibody||Formation (1900), antigen-antibody binding
hypothesis (1938), produced by B cells (1948),
structure (1972), immunoglobulin genes (1976)
|Founder: P Ehrlich|
- Boundless (2016-05-26). "Humoral Immune Response". Boundless. Archived from the original on 2016-10-12. Retrieved 2018-04-01.
- Metchnikoff, Elie (1905) Immunity in infectious disease (full text version) Cambridge University Press
- von Behring E, Kitasato S. (1890) On the acquisition of immunity against diphtheria and tetanus in animals (German). Dtsch. Med. Wochenschr. 16: 1145-1148
- Peer biography by Paul Fildes Biographical Memoirs of Fellows of the Royal Society, Vol. 2, Nov., 1956 (Nov., 1956), pp. 237-247
- hygiene of the sexual life (German, fulltext)
- Mentioned in On the Formation of Specific Anti-Bodies in the Blood, Following Upon Treatment with the Sera of Different Animals, George H. F. Nuttall American Naturalist, Vol. 35, No. 419 (Nov., 1901), pp. 927-932
- Belfanti S. & Carbone T. Produzione di sostanze tossiche mmcl siero di animale inoculati con sangue eterogeneo. Gior. d.r. Accad. di. med. di Torino, Series 4, 46: 321, 1898.
- Bordet, J. 1898. Sur l'agglutination et la dissolution des globules rouges par le serum d'animaux injectes de sang defibrine. Ann. De l'Inst. Pasteur. xii: 688-695.
- Wright, A. E., and S. R. Douglas. 1904. An experimental investigation of the role of the body fluids in connection with phagocytosis. Proc. R. Soc. London 72:357-370.