Why is opsonization important

This results in a much more efficient phagocytosis. The process starts with antibodies of the isotype IgG, IgA, or IgM being made against a surface antigen of the organism or cell to be phagocytosed. The Fab portions of the antibody react with epitopes of the antigen. The Fc portion of secretory IgA can also bind to macrophages and neutrophils for opsonization. The Fab portion of IgG binds to epitopes of an antigen. The Fc portion can now attach the antigen to Fc receptors on phagocytes for enhanced attachment.

This is especially important against encapsulated microbes. C3b and C4b from the complement pathways can also attach antigens to phagocytes. Like IgG, C3b, and to a lesser extent C4b, can function as opsonins, that is, they can attach antigens to phagocytes.

Remember that C3b and C4b are also produced during the alternative complement pathway and the lectin pathway as was discussed in Unit 5. Activation of the complement pathway also promotes inflammation to bring phagocytes and defense chemicals from the bloodstream to the infection site as discussed later under this topic.

C1, consisting of C1q, C1r, and C1s then binds to the Fc portion of the antibodies. The binding of C1q to the antibody molecules activates the C1r portion of C1 which, in turn, activates C1s. This activation gives C1s enzymatic activity to cleave complement protein C4 into C4a and C4b and complement protein C2 into C2a and C2b.

Actually, C3b molecule can bind to pretty much any protein or polysaccharide. In this way, C3b does not interact with our own cells but is able to interact with microbial cells.

Attachment then promotes destruction of the antigen. In vaccines against pneumococccal pneumonia and Haemophilus influenzae type b, it is capsular polysaccharide that is given as the antigen in order to stimulate the body to make opsonizing antibodies against the encapsulated bacterium. The antibody isotype IgE is made against parasitic worms helminths and arthropods. The Fab portions of IgE bind to epitopes on the helminth or arthropod while the Fc portion binds to receptors on eosinophils enabling opsonization.

The inflammatory response then enables phagocytes and defense chemicals to leave the bloodstream and go to the infected site as will be discussed later under this topic. Because of a particular immunodeficiency disorder, a person is unable to produce C3 convertase. Which of the above antibody isotypes could still participate in opsonization? Briefly explain why. As we learned previously, some bacteria by means of the activities described below are able to resist phagocytic attachment :.

The Fab portions of the antibody IgG react with epitopes of the antigen. The Fc portion of IgG can then bind to neutrophils and macrophages thus sticking the antigen to the phagocyte. IgG and IgM can activate the classical complement pathway and C3b or C4b can stick the antigen to phagocytes.

IgE is made against parasitic worms helminths and arthropods. Study the material in this section and then write out the answers to these questions. Do not just click on the answers and write them out. This will not test your understanding of this tutorial. Learning Objectives Discuss how antibodies defend the body by way of opsonization. Include what classes or isotypes of immunoglobulins are involved, the role of the Fab portion of the antibody, the role, if any, of the Fc portion of the antibody, and the role of any complement proteins, if any, involved.

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