IMMUNOLOGY - Roït A. - Mir 2000

Chapter 12. Development of the Immune System in Ontogeny

THE COMPLEMENT SYSTEM

At Cytology/cytology/16.html">Early stages of Organism development, the Blood levels of Complement components are low

An integral part of the innate immune system is The Complement System, which plays a major role in protecting the body against microbes. Approximately 30 different Plasma Proteins belonging to the complement system have been identified (see Chapter 4). They appear during embryonic development and are detected in the blood earlier than IgM (Fig. 12.5). In neonatal serum, their level is 50-60% of that characteristic of an adult organism.

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Fig. 12.5. The diagram shows the earliest dates of the initial appearance of complement system components in human fetal Tissues. By birth, the levels of most of these components exceed 50% of adult levels. In contrast, IMMUNOGLOBULINS begin to be produced by the fetus much later.

The earlier appearance of complement system components in serum compared to IgM reflects the fact that prior to the evolution of Antibodies, complement—along with phagocytes—served as the primary immune defense mechanism in animals. Thus, ontogeny recapitulates phylogeny to a certain extent.



Last update: 13/08/2026

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