lecture 4

VIROLOGY COURSE - BM 330: SEROLOGY OF PLANT VIRUSES

Definition of Serology

  • Serology: The scientific study of blood serum and other bodily fluids.
    • Focuses on the immune system's response.
    • Primarily aims to detect and measure antibodies.
    • Used for diagnosing infections, autoimmune diseases, or checking vaccination status.

Serological Tests

  • Serological Tests: Diagnostic methods to identify antibodies and antigens in animal and plant samples.
    • Antigen: Any foreign protein, such as a virus protein, introduced into an animal (rabbit, mouse, horse, chicken, turkey).
    • Induces the animal to produce antibodies, which are specific proteins circulating in the blood serum.
  • Each antigen has multiple antigenic determinants, which are unique groups of 6-10 amino acids on the antigen's surface.
  • Antiserum: Serum containing antibodies from the animal, producing a mixture known as polyclonal antibodies.
    • Polyclonal antibodies arise from different B cells recognizing multiple epitopes, leading to higher antibody affinity against the antigen.
  • Clonal antibodies: Pure lines of antibodies reacting to a single antigenic determinant.

Production of Antiserum (Antibodies)

A. Immunization, Collection, and Preparation

  • Purified antigen (virus, bacteria, mycoplasmas, etc.) with or without adjuvant:
    • Injection Method: Antigen is injected into the muscle (thigh) or vein (ear) of the animal.
    • Blood Collection: Blood is extracted several weeks or months post-injection from the animal's ear or heart.
    • Clotting: Blood is allowed to clot overnight after which it is centrifuged at 5,000 rpm for 10 minutes, separating the clear antiserum (supernatant) from blood cells (pellet).
    • Storage: Antiserum (serum plus antibodies) is stored in small vials, with glycerin added, and kept frozen.

Hybridomas Cell

  • Definition: A cell formed by fusing an antibody-producing B cell with a mouse myeloma (cancer) cell.
    • Purpose: To produce monoclonal antibodies indefinitely because they can grow continuously in culture.
  • Monoclonal Antibodies: Very specific and may not detect variants of the same virus lacking the specific antigenic determinant responsible for their production.

Serological/Immunological Techniques

  • Types of Serological Tests:
    • Precipitin reaction
    • Agglutination reaction
    • Enzyme-linked immunosorbent assay (ELISA) variants:
    • Double antibody sandwich ELISA (Direct ELISA)
    • Indirect ELISA Test
    • Immunosorbent electron microscopy (ISEM)
    • Ring interface test
    • Microprecipitin test
    • Ouchterlony Double-diffusion test
Precipitin Reaction
  • Antibodies and antigens are mixed in a solution.
    • If a positive match occurs, a band (cloud) will form at the interface in test tubes or drops on a petri dish.
Agglutination Reaction
  • The antigen is adsorbed to the surface of particles (cells, plastids, latex spheres).
    • Addition of antibodies leads to precipitation which demonstrates the reaction.
Enzyme-linked Immunosorbent Assay (ELISA)
  • Widely used by pathologists to detect and study plant viruses.
    • Different variations are implemented to increase sensitivity and ease of use.
  • Double Antibody Sandwich ELISA (Direct ELISA):
    • Procedure:
    1. Add antibodies to the virus into wells of a microtiter plate.
    2. Introduce pure virus or infected plant sap.
    3. Add enzyme-conjugated antibodies against the virus.
    4. Keep substrate (that changes color upon enzyme breakdown) in the well for 30-60 minutes.
    5. Read wells using a colorimeter.
    6. Presence of color indicates the virus's presence in the sample.

Microplate Reader

  • Instrument used for analyzing ELISA results by measuring color intensity, revealing quantitative data about virus concentration.

Indirect ELISA

  • Steps include:
    1. Washing wells after emptying.
    2. Adding colorless substrate and observing changes upon enzyme action.
  • Provides a proportional relationship between color intensity and virus concentration.

Advantages of ELISA

  • Extremely sensitive, allows concurrent testing of large sample numbers.
  • Requires small amounts of antiserum.
  • Results are quantitative, procedures can be semi-automated, and assays function regardless of virus morphology and concentration.

Immunosorbent Electron Microscopy (ISEM)

  • Involves trapping viruses on antibody-coated grids for easy identification with an electron microscope.
  • Distinctive appearance of decorated virus particles aids identification.

Additional Serological Tests

1. Ring Interface Test
  • Dilution of Antigens and Antibodies with appropriate buffers; results are assessed for visible reactions.
2. Ouchterlony Double-Diffusion Test
  • Utilizes agarose gel diffusion for visualization of antigen-antibody interactions.
3. Microprecipitin Test
  • Using a grid with wells for antigen-antibody interaction assessments in a controlled environment.

Uses of Serology

  • Determine relationships between viruses.
  • Identify viruses in plant diseases and symptomless infections.
  • Quantitatively measure virus presence.
  • Locate viruses within cells or tissues and purify them.

Nomenclature of Plant Viruses

  • Many plant viruses are named based on the symptoms caused in their first studied host or based on the host plant infected.
    • Example: Tobacco mosaic virus causes a mosaic on tobacco plants; the disease is also referred to as tobacco mosaic.
    • Tomato spotted wilt virus causes spotted wilt in tomatoes; disease referred to as tomato spotted wilt disease.

Classification of Plant Viruses

  • All viruses belong to the kingdom Viruses, distinguished by:
    1. Type of nucleic acid: RNA viruses, DNA viruses.
    2. Strand details: single-stranded or double-stranded.
    • Types of RNA: ssRNA, dsRNA; Types of DNA: ssDNA, dsDNA.
    1. Morphology: filamentous or isometric.
  • Characteristics include:
    • Replication methods (via polymerase or reverse transcriptase).
    • Viral particle structure (monopartite vs. multipartite genomes).
    • Symmetry of helical structures or protein subunit arrangements in isometric viruses.

Families and Genera of Plant Viruses

  • RNA viruses are classified into families and genera, detailing various types, including tobamoviruses, trichoviruses, and potyviridae, among others.

Control of Plant Viruses

  • Strategies include:
    • Quarantine, inspection, and certification systems to keep viruses out of areas.
    • Eradication strategies for diseased plants.
    • Protecting plants against virus vectors.
    • Use of virus-free seeds and tubers is crucial.
    • Breeding plants for hereditary resistance to viruses is important.
    • Cross Protection: Inoculating plants with a mild virus strain to protect against severe strains.
    • Transgenic plants expressing interference genes to combat virus infections.
    • Heat treatment to inactivate viruses in dormant or actively growing plants.

Assignment Prompt

  • Step-by-step explanation required to detect Tobacco Mosaic Virus in tobacco plants using both Conventional and Quantitative Polymerase Chain Reaction (PCR). Must describe detecting Cauliflower mosaic virus via Conventional PCR as well.
  • Due Date for Electronic Report: 5th February 2026.

Plagiarism Warning

  • Examples include copying or using someone else's work without appropriate citation. Proper citation is necessary when using research findings or formats from others.

Test Information

  • Test Date: 19th February 2026. No acceptable excuses for absence.

Conclusion

  • The study materials emphasize methods for detecting and managing plant viruses, outlining techniques and principles underlying serological and molecular diagnostic approaches.