Human Anatomy & Physiology (9th Edition)

Published by Pearson
ISBN 10: 0321743261
ISBN 13: 978-0-32174-326-8

Chapter 21 - The Immune System: Innate and Adaptive Body Defenses - Review Questions - Page 799: 15


Complements (proteins are a set of 2 plasma proteins that function as part of the body's innate defense mechanism against infection, but also function in specific immunity. Complements opsonize ( identify/mark) antigens or cells to make them more susceptible to lysis, apoptosis or destruction by phagocytes or NK-cells.

Work Step by Step

Certain organisms by the chemical nature of their outer coats attract complement molecules. Once a complement molecule binds with the cell coat of a microbe or cell. Antibodies are not involved in this kind of innate response, which initiate inflammation. In the specific immune response initial antigen-complement reaction produces of complement fractions that attract IgG or IgM antibodies. The binding of the antibodies to the complement-microbe complex causes a cascade of chemical cleavages, and attachments that generates several results--all inimical to the infectious organisms. For example, after the first few complement molecules attach to the coat of the microbe, the antibodies are attracted and bind. This splits the C3 complement molecule into a C3a and a C3b molecules. C3b binds to the complex which is then joined by C5 complement molecule . The cascade continues as C5 splits into C5a and C5b. C5a leaves but C5b adheres to the growing complex. This growing complex attracts in turn C6, C7, C8 and C9 complement molecules. This large complex forms a ringlike structure which pierces the surface of the antigenic cell. Ultimately the antigenic cell is destroyed by lysis. Opsonins ( complement derivatives) can identify cells or microbes for destruction by phagocytosis or lysis. They can also enhance chemotaxis or inflammatory responses.
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