Antibodies, also known as immunoglobulins, are Y-shaped proteins produced by plasma cells that are used by the immune system to neutralize pathogens such as bacteria and viruses. Antibodies recognize a unique molecule of the pathogen, called an antigen, and subsequently neutralize or eliminate the pathogen. In this article, we will examine antibodies in more depth by looking at their structure, function, and role in the immune response.
The Structure of Antibodies
Antibodies are composed of basic structural units called immunoglobulin domains. Each antibody contains two heavy chains and two light chains that are linked together by disulfide bonds. The light chains are of two types – kappa and lambda. The N-terminal ends of the antibody, termed the Fab region, contain the antigen binding site made of variable domains from the heavy and light chains. The constant regions that make up the tail end, known as the Fc region, mediate immune responses like opsonization and complement activation.
The variable domains are responsible for the tremendous diversity of Antibodies as each one can bind to a unique antigen. There are an estimated 10^14 different antibody structures possible, allowing the immune system to recognize virtually any foreign molecule. The constant regions interact with other immune cells and molecules to trigger immune functions. Overall, the structure enables antibodies to identify pathogens through the Fab region and mount immune attacks through the Fc region.
Function and Specificity of Different Antibody Classes
There are five classes of antibodies in humans – IgA, IgD, IgE, IgG, and IgM. They differ in their structure and functions.
IgG is the most abundant antibody, making up about 75% of serum antibodies. It plays a major role in fighting bacterial and viral infections. IgM is the first antibody produced during initial infections. It activates complement pathways for swift killing of pathogens.
IgA antibodies are found in secretions like tears, saliva, and breast milk where they provide mucosal immunity against infections. IgE antibodies mediate allergic reactions and protect against parasites. IgD is found on B cell surfaces and has an unknown function currently.
Each antibody class has attributes tuned for different roles such as activating immune cells, neutralizing toxins, and promoting phagocytosis. The specificity comes from the diverse recognition sites on their Fab regions, allowing highly tailored responses against specific microbes.
The Immune Response and Generation of Antibody Diversity
When a pathogen first enters the body, various immune cells recognize signature pathogen molecules through pattern recognition receptors. This leads to their activation and initiation of the adaptive immune response by B and T cells.
B cells produce antibodies. Each B cell expresses antibody proteins with a single antigen binding specificity on their surface. If a B cell encounters a pathogen that matches its binding site, it begins proliferating rapidly. The clone expands into either memory B cells for long-term protection or plasma B cells.
Plasma B cells mass produce and secrete antibodies of identical specificity into the bloodstream and tissues. These antibodies then neutralize the pathogen directly or tag it for elimination by other immune cells.
The tremendous diversity of antibody binding sites arises from genetic events during B cell development in the bone marrow. V(D)J recombination randomly combines gene segments that encode the 6 variable domains, generating 10^18 potential specificities. Further hypermutations in the activated B cells help fine-tune the binding. This array of genetic events coupled with competitive selection enables generation of antibodies against nearly any antigen.
In summary, antibodies are a core component of our adaptive immunity and form the basis of humoral immunity. Through their highly evolved structure, diverse specificities, and finely orchestrated production via B cells, antibodies enable the immune system to robustly recognize and eliminate diverse pathogens. By understanding antibodies and harnessing their potential through modern biotechnology, we are empowering new diagnostics and therapies against infectious diseases and cancers.
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it