Antibody

Antibodies, or immunoglobulins (Ig), are Y-shaped proteins produced by B cells of the immune system. They play a crucial role in identifying and neutralizing foreign substances such as bacteria, viruses, and toxins. Antibodies are also widely used in research, diagnostics, and therapeutic applications.

Structure of an Antibody

1. Fab Region (Fragment, Antigen-Binding)
   • Contains the variable regions that bind to specific antigens.
   • The variability allows antibodies to recognize diverse antigens.
2. Fc Region (Fragment, Crystallizable)
   • Responsible for interacting with immune cells and activating the immune system.
   • Determines the antibody’s class (e.g., IgG, IgA).

Types of Antibodies

1. Monoclonal Antibodies (mAbs)
   • Derived from a single clone of B cells.
   • Highly specific to a single epitope of an antigen.
   • Applications: Therapeutics (e.g., cancer immunotherapy), diagnostics.
2. Polyclonal Antibodies (pAbs)
   • Produced by multiple B cell clones.
   • Recognize multiple epitopes on the same antigen.
   • Applications: Research, as they provide robust signal in detection assays.
3. Recombinant Antibodies
   • Engineered in vitro for high specificity and consistency.
   • Often humanized or fully human in therapeutic applications.
4. Primary Antibodies
   • Directly bind to the antigen of interest.
   • Used in assays like Western blot, ELISA, and immunofluorescence.
5. Secondary Antibodies
   • Bind to primary antibodies to amplify the signal.
   • Often conjugated to enzymes (e.g., HRP, AP) or fluorophores for detection.

Antibody Classes

1. IgG
   • Most abundant in blood and extracellular fluid.
   • Provides long-term immunity after infection or vaccination.
2. IgA
   • Found in mucosal areas (e.g., respiratory and gastrointestinal tracts).
   • Provides localized protection.
3. IgM
   • First antibody produced during an immune response.
   • Effective in forming antigen-antibody complexes.
4. IgE
   • Involved in allergic reactions and responses to parasites.
5. IgD
   • Functions in B cell activation.

Applications of Antibodies

1. Research Tools
   • Protein detection (e.g., Western blot, immunohistochemistry).
   • Cell sorting (e.g., flow cytometry).
   • Antigen quantification (e.g., ELISA).
2. Diagnostics
   • Identifying infections, diseases, and biomarkers.
   • Rapid tests (e.g., COVID-19 antigen tests).
3. Therapeutics
   • Cancer treatment (e.g., immune checkpoint inhibitors like pembrolizumab).
   • Autoimmune diseases (e.g., monoclonal antibodies targeting inflammatory pathways).
   • Vaccines (e.g., antibodies for passive immunity)