26: Diagnosing Infections

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Page ID: 144234

Ying Liu, Serena Chang, Grace Murphy, Esther Ajayi-Akinsulire, Isobel Ardren, Izabella Guy, Kai Johnston, Saskia Lee, and Lauren Russell
City College of San Francisco

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Many laboratory tests are designed to confirm a presumptive diagnosis by detecting antibodies specific to a suspected pathogen. Unfortunately, many such tests are time-consuming and expensive. That is now changing, however, with the development of new, miniaturized technologies that are fast and inexpensive. For example, researchers at Columbia University are developing a “lab-on-a-chip” technology that will test a single drop of blood for 15 different infectious diseases, including HIV and syphilis, in a matter of minutes.¹ The blood is pulled through tiny capillaries into reaction chambers where the patient’s antibodies mix with reagents. A chip reader that attaches to a cell phone analyzes the results and sends them to the patient’s healthcare provider. Currently the device is being field tested in Rwanda to check pregnant women for chronic diseases. Researchers estimate that the chip readers will sell for about $100 and individual chips for $1.²

Picture of a computer chip. — Figure $\PageIndex{1}$: Lab-on-a-chip technology allows immunological assays to be miniaturized so tests can be done rapidly with minimum quantities of expensive reagents. The chips contain tiny flow tubes to allow movement of fluids by capillary action, reactions sites with embedded reagents, and data output through electronic sensors. (credit: modification of work by Maggie Bartlett, NHGRI)

26.1: Polyclonal Antibodies
In addition to being crucial for our normal immune response, antibodies provide powerful tools for research and diagnostic purposes. The high specificity of antibodies makes them an excellent tool for detecting and quantifying a broad array of targets, from drugs to serum proteins to microorganisms. With in vitro assays, antibodies can be used to precipitate soluble antigens, agglutinate cells, and neutralize drugs, toxins, and viruses.
26.2: Monoclonal Antibodies
This page discusses monoclonal antibodies (mAbs), which are characterized by their high specificity and produced by fusing mouse B cells with myeloma cells. While effective for cancer treatment, the methods are costly. Humanized mAbs minimize immune reactions and show potential in therapies like Herceptin, but their high price restricts use against infectious diseases. Research is ongoing into using genetically engineered plants for mAb production to create more cost-effective clinical options.
26.3: In vitro Assays
Laboratory tests to detect antibodies and antigens outside of the body (e.g., in a test tube) are called in vitro assays. When both antibodies and their corresponding antigens are present in a solution, we can often observe a precipitation reaction in which large complexes (lattices) form and settle out of solution. In the next several sections, we will discuss several common in vitro assays.
26.4: Agglutination Assays
This page details agglutination tests for disease diagnosis and blood typing. Direct agglutination clumps cells using specific antibodies, while indirect agglutination employs beads for visualization. Developed by Rebecca Lancefield, these tests can quickly diagnose diseases like typhoid fever, especially in low-resource settings.
26.5: Enzyme Immunoassays (EIA) and Enzyme-Linked Immunosorbent Assays (ELISA)
This page details various immunoassay techniques, emphasizing enzyme immunoassays (EIAs) and enzyme-linked immunosorbent assays (ELISAs) for antigen and antibody detection. It covers different ELISA methods (direct, indirect, sandwich) and other techniques such as immunohistochemistry. Additionally, it addresses MMR titer tests for healthcare workers' immunity verification.
26.6: Fluorescent Antibody Techniques
Rapid visualization of bacteria from a clinical sample such as a throat swab or sputum can be achieved through fluorescent antibody (FA) techniques that attach a fluorescent marker (fluorogen) to the constant region of an antibody, resulting in a reporter molecule that is quick to use, easy to see or measure, and able to bind to target markers with high specificity. We can also label cells, allowing us to precisely quantify particular subsets of cells or even purify them for further research.
26.E: Laboratory Analysis of the Immune Response (Exercises)

Footnotes

1 Chin, Curtis D. et al., “Mobile Device for Disease Diagnosis and Data Tracking in Resource-Limited Settings,” Clinical Chemistry 59, no. 4 (2013): 629-40.
2 Evarts, H., “Fast, Low-Cost Device Uses the Cloud to Speed Up Testing for HIV and More,” January 24, 2013. Accessed July 14, 2016. http://engineering.columbia.edu/fast...g-hiv-and-more.

Thumbnail: Enzyme-linked antibodies against CD8 were used to stain the CD8 cells in this preparation of bone marrow using a chromogen. (credit: modification of work by Yamashita M, Fujii Y, Ozaki K, Urano Y, Iwasa M, Nakamura S, Fujii S, Abe M, Sato Y, Yoshino T).

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