Antigen-Antibody interactions and detection

Who demonstrated in 1890 that serum transfer from immunized animals could cure diphtheria?

Emil von Behring and Shibasabura Kitasato.

Who first described plasma B cells as responsible for antibody generation?

Astrid Fagraeus in 1948.

Who developed the clonal selection theory in 1957?

Frank Burnet and David Talmage.

Who published the molecular structure of antibodies in 1959?

Gerald Edelman and Rodney Porter.

Who discovered the role of the Bursa of Fabricius in antibody production in birds?

Bruce Glick and Timothy Chang in 1979.

What is an antibody?

A molecule that binds to specific targets (antigens) and tags them for destruction.

What is an antigen?

A foreign substance that triggers an immune response.

What is an epitope?

A specific region within an antigen that can trigger an antibody response.

What is a linear epitope?

An epitope made of adjacent amino acids in a peptide chain.

What is a discontinuous epitope?

An epitope formed by amino acids located in different parts of a protein chain.

What does it mean if an antibody binds to a denatured protein?

It recognizes a linear epitope.

What is specificity in antibody-antigen interaction?

The ability of an antibody’s variable region to react with only one epitope.

What is cross-reactivity?

When an antibody against one antigen interacts to some degree with a different antigen.

Why does cross-reactivity occur?

Because two epitopes share structural similarities.

What is affinity?

The strength of binding between an antibody’s variable region and its epitope.

What is avidity?

The overall strength of all antibody-epitope interactions combined.

What determines the detection method for antigen-antibody interaction?

The physical form or size of the antigen.

What test detects particulate antigen-antibody interactions?

Agglutination test.

What is haemagglutination?

Agglutination reaction involving red blood cell surface antigens.

What is a qualitative agglutination test used for?

Detecting the presence of specific antigens or antibodies (e.g., blood typing).

What is a quantitative agglutination test used for?

Measuring the concentration of antigen or antibody using serial dilutions.

What is a precipitation reaction?

A reaction between soluble antigens and antibodies forming an insoluble precipitate.

When does visible precipitation occur?

When antigen and antibody are at optimal proportions (zone of equivalence).

What is a gel precipitation assay?

A test where antigen and antibody diffuse in agar to form a visible precipitation line.

What are polyclonal antibodies?

A mixture of antibodies produced by different plasma cell clones, recognizing multiple epitopes.

What factors affect polyclonal antibody production?

Antigen dose, animal size, and immunogenicity.

What is immunogenicity?

The ability of an antigen to trigger an immune response.

Why must haptens be conjugated to carriers?

Because molecules <10 kDa are poorly immunogenic and need carriers to induce a response.

What is an adjuvant?

A substance added to antigens to enhance the immune response.

How do adjuvants enhance immune responses?

By stimulating innate immune receptors (PAMPs) and improving APC activation.

What are ISCOMs?

Immune-stimulating micelles that help viral proteins enter APCs for better antigen presentation.

What causes serum sickness?

Reaction to foreign animal antibodies used therapeutically.

What are symptoms of serum sickness?

Fever, rash, itching, swollen lymph nodes, and painful joints.

What is the main conclusion from serum sickness observations?

Antibody therapy is effective but should minimize foreignness.

What are monoclonal antibodies?

Identical antibodies from a single plasma cell clone with the same specificity.

How are hybridomas made?

By fusing antibody-producing B cells with myeloma cells.

What is the role of HAT medium in hybridoma production?

To select for fused hybridoma cells only.

What are chimeric antibodies?

Antibodies with mouse antigen-binding regions and human constant regions.

What are humanized antibodies?

Antibodies that retain only the mouse hypervariable regions but are mostly human (>90%).

What is Protein A Sepharose used for?

Purifying IgG, IgA, and IgM antibodies via affinity binding.

What is Protein G Sepharose used for?

Purifying IgG antibodies by affinity chromatography.

How are labeled antibodies used in detection?

By conjugating antibodies with enzymes or fluorescent dyes for visualization.

What is ELISA used for?

Detecting specific antigens or antibodies in serum or culture samples.

What is immunohistochemistry (IHC)?

A method for detecting specific antigens in tissues using labeled antibodies.

What enzymes are commonly used in conjugated antibodies?

Horseradish peroxidase (HRP) and alkaline phosphatase (ALK).

What are common fluorescent dyes used in immunofluorescence?

FITC (green) and PE (red).

What does flow cytometry detect?

Fluorescence-labeled cells to identify and sort cell populations.

What markers identify T cells and T helper cells?

CD3 for all T cells; CD4 for helper T cells and monocytes.

Name three main applications of antibodies.

Identification, clinical diagnosis, and therapy.

How are antibodies used in disease diagnosis?

By detecting specific antigenic markers (e.g., ANA for SLE).

How are antibodies used in therapy?

To block harmful molecules (e.g., anti-TNFα for rheumatoid arthritis).

How can antibodies be used in research?

To study or manipulate cell functions (e.g., blocking IL-12 to stop lymphocyte proliferation).