Antigens & Antibodies: reactions, detection, and applications

Introduction

Adaptive immune responses are not directed against whole bacteria, protozoa, or viruses, but instead against portions of cells, viruses, and even parts of single molecules that the body recognizes as foreign and worthy of attack.

These biochemical shapes are called antigens

Adaptive Immunity Crash Course

Antigens & Antibodies

antigens stimulate the production of one or more antibodies by white blood cells. The term originally came from antibody generator

Antigens are “molecules of attack”. Our bodies respond to foreign antigens associated with pathogenic bacteria/viruses/etc. rather than the pathogen itself

Antigens & Antibodies

Antibodies (Ab), or immunoglobulins (Ig), are large Y-shaped proteins produced by B-cells in response to the presence of an antigen.

Antibodies bind to antigens and aid in defense of the body by neutralizing the pathogens possessing the antigens that stimulated their production

Actions of Antibodies

Antigens & Antibodies

Each antibody binds to a specific antigen by way of an interaction similar to the fit between a lock and a key.

Antibodies bind to antigens forming immune complexes or antibody-antigen complexes.

Applications

Antigen/Antibody Applications

Antigens and Antibodies have many uses in Biotech applications Medical Diagnostics

Vaccine Production

Locating Cellular Proteins

Immunoprecipitation

ELISA

Medical Diagnostics

Detection of particular antibodies is a very common form of medical diagnostics

In biochemical assays for disease diagnosis, a titer of antibodies directed against Epstein-Barr virus  is estimated from the blood. If those antibodies are not present, either the person is not infected, or the infection occurred a very long time ago, and the B cells generating these specific antibodies have naturally decayed.

Medical Diagnostics

Antibodies raised against human chorionic gonadotropin (HCG) are used in over the counter pregnancy tests

These tests often work by using immunochromatography to detect the presence of HCG.

Immunochromotography

Test strips use antibodies to capture a molecule of interest (i.e. HCG). Accumulation of the molecule of interest causes a color change on the test strip, indicating a positive result.

Vaccine Production

A vaccine is a biological preparation that improves immunity to a particular disease.

Vaccines typically contain an agent that resembles a disease-causing microorganism

We can isolate antigenic surface proteins of pathogens and use them to produce vaccines and generate immunity.

Locating Proteins

Antibodies linked to fluorescent molecules can be used to locate proteins within cells and can be used to differentiate between cell types based on what proteins the cells are expressing.

Immunofluorescence image of the eukaryotic cytoskeleton. Actin filaments are

shown in red, microtubules in green, and the nuclei in blue.

Immunoprecipitation

Is the technique of precipitating a protein antigen out of solution using an antibody that specifically binds to that particular protein.

This is often used to isolate and concentrate a particular protein from a sample containing many different proteins.

Immunoprecipitation

ELISA

Enzyme-linked immunosorbent assay (ELISA) is a test that uses antibodies and color change to identify a substance.

ELISA

Antigens from a sample are attached to a surface (usually they are immobilized by binding to embedded antibodies).

A further specific antibody is applied over the surface so it can bind to the antigen. This antibody is linked to an enzyme

ELISA

In the final step, a substance containing the enzyme's substrate is added. The enzymes reaction with its substrate produces a detectable signal, most commonly a color change in the substrate

ELISA

ELISA

The ELISA can been useful as a diagnostic tool in medicine to check for the presence of certain antigens

ELISA is also often used for quality-control in various industries (i.e. ELISA can be used to check for the presence of allergens in food).