Brock Biology of Microorganisms (15th Edition)
15th Edition
ISBN: 9780134261928
Author: Michael T. Madigan, Kelly S. Bender, Daniel H. Buckley, W. Matthew Sattley, David A. Stahl
Publisher: PEARSON
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Chapter 26.6, Problem 1CR
Innate recognition of common pathogens occurs through pathogen-associated molecular patterns (PAMPs). Phagocytes recognize PAMPs through preformed pattern recognition receptors (PRRs). The recognition and interaction process stimulates phagocytes to destroy the pathogens through a signal transduction mechanism that induces phagocytosis of the infectious agent.
Identify some PAMPs that are recognized by PRRs. Which cells express PRRs? How do PRRs associate with PAMPs to promote innate immunity?
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The classical complement pathway is initiated by C1q binding to the surface of a pathogen. In some cases, C1q can directly bind the pathogen, for instance by recognizing proteins of bacterial cell walls, but in most cases C1q binds to IgM antibodies that are bound to the pathogen surface. How does this IgM-binding feature of C1q contribute to rapid, innate immune responses rather than to slow, adaptive responses?
C1q induces B lymphocytes to begin secreting antibody within hours of pathogen exposure.
Natural antibody that binds to many microbial pathogens is produced prior to pathogen exposure.
C1q binds to C-reactive protein which then binds to IgM on the pathogen surface.
C1q directly induces inflammation, recruiting phagocytes and antibodies from the blood into the infected tissue.
C1q binds to dendritic cells in the infected tissue, inducing them to secrete inflammatory cytokines.
IgM antibodies are much more efficient than IgG at activating the complement cascade. However, under certain circumstances, IgG
antibodies will activate the complement pathway. One example of a situation in which IgG binding to its antigen will not trigger the
complement cascade is when
the IgG antibodies are neutralizing a bacterial toxin protein by blocking the receptor-attachment site on the toxin.
the IgG antibodies are binding self-antigens, such as chromatin released from dead cells.
the IgG antibodies bind to a bacterial surface by recognizing a repetitive polysaccharide component of the bacterial capsule.
the IgG antibodies bind to a viral capsid protein that is present in more than 100 copies on the viral particle surface.
The alternative pathway is an amplification loop for C3b formation that is accelerated by properdin in the presence of pathogens. The alternative pathway of complement activation has an important role in innate immunity, due to its ability to greatly amplify the amount of C3b deposited onto the pathogen surface. This amplification occurs because:
The C3 convertase of the alternative pathway is much more active than those of the classical and lectin pathways.
The C3 convertase of the alternative pathway works as a soluble enzyme in the plasma.
The C3 convertase of the alternative pathway cannot be inactivated by complement regulatory factors in the host.
The C3 convertase of the alternative pathway is more efficiently recruited to pathogen surfaces than the C3 convertases of the classical and lectin pathways.
The C3 convertase of the alternative pathway contains C3b, and can generate more of itself.
Chapter 26 Solutions
Brock Biology of Microorganisms (15th Edition)
Ch. 26.1 - What major class of immune cells mediates an...Ch. 26.1 - Prob. 2MQCh. 26.1 - Compare and contrast the major features of innate...Ch. 26.2 - Describe host tissue specificity for pathogens.Ch. 26.2 - Identify physical and chemical barriers to...Ch. 26.2 - What other factors may control the outcome of an...Ch. 26.2 - Identify at least four mechanisms by which a...Ch. 26.3 - Describe the circulation of a leukocyte from the...Ch. 26.3 - What soluble molecules determine whether a...Ch. 26.3 - Cells involved in innate and adaptive immunity...
Ch. 26.4 - How does the development of B, T, and NK cells...Ch. 26.4 - Distinguish between the primary lymphoid organs...Ch. 26.4 - Leukocytes are differentiated white blood cells...Ch. 26.5 - Although technically not part of the immune...Ch. 26.5 - Describe the mechanisms by which circulating...Ch. 26.5 - Pathogens may colonize host tissues when...Ch. 26.6 - Identify a PAMP shared by a group of...Ch. 26.6 - Outline the general features of a signal...Ch. 26.6 - Innate recognition of common pathogens occurs...Ch. 26.7 - Identify the mechanism used by phagocytes to...Ch. 26.7 - Describe several reasons why phagocytes are not...Ch. 26.7 - Phagocytosis is the engulfing of infectious...Ch. 26.8 - Prob. 1MQCh. 26.8 - Identify the major symptoms of localized...Ch. 26.8 - Fever and inflammation, characterized by pain,...Ch. 26.9 - In what ways does the classical pathway of...Ch. 26.9 - What is opsonization, and how does opsonization...Ch. 26.9 - Why are the mannose-binding lectin and alternative...Ch. 26.9 - The complement system is composed of soluble...Ch. 26.10 - Prob. 1MQCh. 26.10 - Prob. 2MQCh. 26.10 - Prob. 1CRCh. 26 - Prob. 1AQCh. 26 - Describe the potential problems that would arise...Ch. 26 - Prob. 3AQCh. 26 - Prob. 4AQ
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- B cells express a complement receptor that binds to C3b cleavage products, such as iC3b and C3dg. When a B cell with an antigen receptor that specifically recognizes that pathogen also has its complement receptor stimulated because the pathogen is opsonized with these C3 fragments, B cell activation is greatly enhanced. Due to this mechanism, B cells can be activated by much lower concentrations of antigen (in this case, the pathogen) than if the antigen is devoid of complement components. This mechanism functions to: Ensure that pathogens are readily detected by the adaptive immune system before they replicate to high levels in the host Prevent B cells from being activated in response to antigens that are not pathogens Allow B cells to phagocytose the pathogen and help destroy it Induce increased rounds of B cell replication to make more pathogen-specific B cells Allow the B cell to block pathogen replication by interfering with multiple pathogen surface functionsarrow_forwardThe terminal complement proteins polymerize to form pores in membranes that can kill certain pathogens. The terminal components of the complement pathway assemble to form a membrane attack complex that can induce pathogen lysis and death. Yet, evidence indicates that this feature of complement is less important than the earlier steps that promote pathogen opsonization and induce inflammation. This conclusion is based on: In vitro experiments showing that very few species of bacteria are susceptible to lysis by the membrane attack complex Experiments indicating that only bacteria, but not viruses or fungi, are susceptible to lysis by the membrane attack complex The very low levels of terminal complement components in the serum The fact that other mammalian species lack the terminal components of the complement pathway needed to form the membrane attack complex The limited susceptibility to infections of patients with deficiencies in terminal complement componentsarrow_forwardOpsonization of pathogens by both antibodies and complement proteins (C3b) leads to uptake and destruction of the pathogen by phagocytic cells that express both Fc receptors and complement receptors. Which of the following in the figure below is the most efficient form of dual opsonization of the pathogen by antibody and C3b to maximize phagocytosis?arrow_forward
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