Direct Test Labeled anti-X antibody Detectable marker Wash off Positive result Label detected. unbound antibodies. Test for label. Conclusion: Antigen X is present. Labeled antibodies bind to antigen. Labeled antibodies remain. Unknown Add labeled antigen antibodies specific for antigen X. Unknown antigen is attached to a solid surface. Wash off unbound antibodies. Negative result Label not detected. Test for label. Labeled antibodies do not bind. Labeled antibodies washed off. Conclusion: Antigen X is not present (a) Indirect Test Detectable marker Labeled anti-human Patient's Add labeled IgG antibody antibody (IgG) secondary antibodies (anti-human IgG); wash off any that do not bind. Wash off unbound Test for Positive result Label detected. Conclusion: Patient's serum has IgG against antigen X. label, antibodies. Patient's antibodies bind to antigen. Patient's antibodies remain. Labeled secondary antibodies bind to patient's IgG and remain. Add patient's Antigen X serum (contains antibodies). Add labeled secondary antibodies (anti-human IgG); wash off any that do not bind. Antigen X is attached to a solid surface. Wash off unbound antibodies. Test for Negative result label. Label not detected. Conclusion: Patient's serum does not have IgG against antigen X. Patient's antibodies do not bind. Patient's antibodies washed off. No human IgG, present so labeled secondary antibodies do not bind. (b) FIGURE 18.5 Basic Principles of Tests That Use Labeled Antibodies to Detect Antigen-Antibody Interactions (a) Positive and negative results of a direct test. (b) Positive and negative results of an indirect test.
Direct Test Labeled anti-X antibody Detectable marker Wash off Positive result Label detected. unbound antibodies. Test for label. Conclusion: Antigen X is present. Labeled antibodies bind to antigen. Labeled antibodies remain. Unknown Add labeled antigen antibodies specific for antigen X. Unknown antigen is attached to a solid surface. Wash off unbound antibodies. Negative result Label not detected. Test for label. Labeled antibodies do not bind. Labeled antibodies washed off. Conclusion: Antigen X is not present (a) Indirect Test Detectable marker Labeled anti-human Patient's Add labeled IgG antibody antibody (IgG) secondary antibodies (anti-human IgG); wash off any that do not bind. Wash off unbound Test for Positive result Label detected. Conclusion: Patient's serum has IgG against antigen X. label, antibodies. Patient's antibodies bind to antigen. Patient's antibodies remain. Labeled secondary antibodies bind to patient's IgG and remain. Add patient's Antigen X serum (contains antibodies). Add labeled secondary antibodies (anti-human IgG); wash off any that do not bind. Antigen X is attached to a solid surface. Wash off unbound antibodies. Test for Negative result label. Label not detected. Conclusion: Patient's serum does not have IgG against antigen X. Patient's antibodies do not bind. Patient's antibodies washed off. No human IgG, present so labeled secondary antibodies do not bind. (b) FIGURE 18.5 Basic Principles of Tests That Use Labeled Antibodies to Detect Antigen-Antibody Interactions (a) Positive and negative results of a direct test. (b) Positive and negative results of an indirect test.
Chapter16: Antifungal, Antiviral, And Immunizing Agents
Section: Chapter Questions
Problem 24RQ
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In (b), why would it be more efficient to use labeled anti-human IgG rather than label the patient’s antibodies?
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