Question

Match the antibody class with its description. _______ IgA \(\quad\) A. This class of antibody is the only one that can cross the placenta. _________ IgD \(\quad\) B. This class of antibody is the first to appear after activation of B cells. _________ IgE \(\quad \mathrm{C}\). This class of antibody is involved in the defense against parasitic infections and involved in allergic responses. _________ IgG \(\quad \mathrm{D}\). This class of antibody is found in very large amounts in mucus secretions. __________ IgM \(\quad E\). This class of antibody is not secreted by B cells but is expressed on the surface of naive B cells.

Short answer

IgA-D, IgD-E, IgE-C, IgG-A, IgM-B

Step-by-step solution

- Identify the function of IgA

IgA is an antibody that is typically found in mucus secretions such as saliva, tears, and secretions of the respiratory and gastrointestinal tracts. Its main function is to prevent colonization by pathogens. Therefore, IgA matches with description D.

- Match IgD with its description

IgD is an antibody that is expressed on the surface of naive B cells and is not secreted in a significant amount. Its primary role is in the activation of B cells. IgD matches with description E.

- Identify the role of IgE

IgE is known for its involvement in allergic responses and its function in defense against parasitic infections. Hence, IgE matches with description C.

- Determine the importance of IgG

IgG is the most prevalent antibody in blood circulation and is the only class of antibody that can cross the placenta to provide protection to the developing fetus. Therefore, IgG corresponds to description A.

- Define the characteristics of IgM

IgM is the first antibody to appear in response to initial exposure to antigen. This class of antibody is produced by B cells before they switch to making other types of antibodies. Therefore, IgM aligns with description B.

Key concepts

IgA and Pathogen Defense

Immunoglobulin A (IgA) plays a critical role in the defense mechanisms of the body, specifically at mucosal surfaces. It is abundantly present in saliva, tears, and secretions of the respiratory and gastrointestinal tracts, where it serves as a first line of defense by neutralizing and preventing pathogens from adhering to and penetrating the mucous membranes.

IgA operates by binding to the antigens on the surface of pathogens, which include bacteria, viruses, and toxins, and blocks their ability to infect. This process is known as immune exclusion. Additionally, IgA can be a part of the immune response that neutralizes toxins and immobilizes microbes, facilitating their removal from the body.

IgD and B Cell Activation

Immunoglobulin D (IgD) has a less understood role compared to other immunoglobulins, but it is essential for the maturation and sensitivity of B cells. Found on the surface of B cells, IgD aids in the activation of these cells when an antigen presents itself. Upon antigen binding, IgD signals the B cells to activate and produce antibodies that are specific to that antigen.

IgD's presence on the naive B cells also serves as a marker for the differentiation of B cells during their development. This immunoglobulin participates in the initiation of the primary immune response and is vital for maintaining surveillance against potential threats.

IgE in Allergic Responses

Immunoglobulin E (IgE) is well-known for its role in allergic responses and defense against parasitic infections. It is associated with allergy symptoms because it triggers the release of histamine and other chemicals from mast cells and basophils when it binds to allergens. This reaction results in inflammation and symptoms seen in conditions such as hay fever, asthma, and anaphylaxis.

In addition to its role in allergies, IgE also protects the body from parasites such as worms by activating eosinophils and other cells that are capable of attacking these larger pathogens. This aspect of IgE's function is more prominent in areas where parasitic infections are common.

IgG Placental Transfer

Immunoglobulin G (IgG) is the most abundant type of antibody in the human body and is critical for long-term immunity. It is the only antibody that can cross the placenta from mother to fetus. This transfer provides the developing baby with passive immunity, giving protection against pathogens present in the mother's environment until the newborn's own immune system develops fully.

The ability to cross the placenta is attributed to IgG's structure, allowing it to be transported by cells in the placenta that then transfer it to the fetal circulation. This immunoglobulin not only provides immediate protection but also plays a role in forming the baby's immune memory.

IgM and Primary Immune Response

Immunoglobulin M (IgM) is the first antibody to be produced in response to an initial encounter with an antigen. This pentameric antibody is effective in eliminating pathogens during the early stages of the primary immune response before there is sufficient IgG. IgM's large size and multivalency allow it to bind strongly to the antigens, effectively agglutinating and neutralizing them.

As the frontline defender, IgM is critical for the initial phases of host defense and is also crucial in activating the complement system, which enhances the ability to clear pathogens from the bloodstream and tissues.