Helper T-cells

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Immunology

Summary

Helper T cells, which start off as naive T cells, demonstrate remarkable versatility in the immune response and can differentiate into distinct subtypes: Th-1, Th-2, and Th-17, in response to specific cytokines released by antigen-presenting cells (APCs). Th-1 cells differentiate when APCs release IL-12 and IFN-γ, enabling them to combat intracellular pathogens by producing cytokines like IFN-γ and IL-2, which activate macrophages and killer T cells. However, Th-1 cells have also been implicated in certain disease states, like autoimmune diseases and chronic inflammatory conditions. Th-2 cells are produced when APCs release IL-4 and play a role in fighting helminths by releasing cytokines like IL-4 and IL-5, which activate eosinophils, mast cells, IgE, and macrophages. Conversely, Th-2 cells have also been linked to allergic reactions. Th-17 cells fight extracellular pathogens by releasing cytokines IL-17 and IL-22, triggering neutrophil recruitment. However, Th-17 cells have also been implicated in autoimmune diseases like psoriasis and rheumatoid arthritis.

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FAQs

What is the basic physical structure of antibodies?

Antibodies, also known as immunoglobulins, have a characteristic 'Y' shape. They are composed of four polypeptide chains: two identical heavy (H) chains and two identical light (L) chains. Each chain comprises a variable region (involved in antigen binding) and a constant region. The antigen-binding site, formed by the variable regions of the heavy and light chains, is known as a paratope. The region of an antigen recognized by the antibody is known as an epitope.

How does the fragment antigen binding (Fab) work in the antibody structure?

The Fab, or Fragment Antigen Binding, region of the antibody includes a portion of both the heavy and light chains. This region is responsible for binding to the antigen. Each Fab fragment contains an antigen-binding site, comprising a variable region that can change to bind specifically to the antigen's epitope. This is why antibodies can recognize and bind to a vast number of different antigens.

What is the role of the fragment crystallizable (Fc) region in the antibody structure?

The Fc, or Fragment Crystallizable, region of an antibody is formed by the tail region that stems from the lower portion of the 'Y' structure. This region, unlike the Fab region, does not bind to antigens. Instead, it interacts with effector cells and complement proteins to mediate immunological responses. The Fc region allows antibodies to activate immune system cells or directly kill the pathogen.

What is the difference between bound antibodies and secreted antibodies?

Bound antibodies, also known as antigen receptors, are bound to the surface of B cells and are used to recognize antigens. Once an antigen binds to the antigen receptor, it triggers the B cell to respond. On the other hand, secreted antibodies are not bound to the B cell membrane, but are instead released into the body fluids (blood, saliva, etc.). These antibodies can then freely circulate to bind with antigens and help neutralize them.

How do affinity and avidity contribute to antibody function?

Both affinity and avidity are key concepts in understanding the effectiveness of antibody-antigen binding. Affinity refers to the strength of a single bond between an antibody's Fab region and an epitope on the antigen. Higher affinity implies a stronger, more effective bond. Avidity refers to the cumulative strength of multiple affinities, and this can significantly enhance the overall stability of the antigen-antibody interaction, particularly when multiple epitopes are present on the same antigen.

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