Antibody Classes & Functions

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Immunology

Summary

The immune system employs five specialized classes of antibodies: IgM, IgG, IgA, IgE, and IgD, each tailored for specific defense roles. IgM is the first antibody produced by activated naive B-cells during initial pathogen exposure. Present in pentameric or hexameric forms, IgM can be attached to the cell surface or secreted into the blood and lymph, notably initiating the classical complement pathway to amplify immune reactions. IgG, the most abundant antibody in blood, is produced by plasma cells. Unique in its ability to cross the placenta, it grants newborns temporary immunity. It specializes in opsonization, marking pathogens for destruction, and facilitates antibody-dependent cellular cytotoxicity (ADCC). IgA is primarily responsible for mucosal immunity. Concentrated in the GI, respiratory, and genitourinary tracts, its dimeric form helps it resist those harsh environments. By agglutinating pathogens, it aids their expulsion via mucus or stool. IgA is also secreted in breast milk, providing protection to the GI tracts of infants. IgE, though less abundant, is vital against parasitic invasions, especially helminth infections. IgE is also responsible for mast cell degranulation, allergies and anaphylaxis, and type 1 hypersensitivity reactions. Finally, IgD, often seen co-expressed alongside IgM on mature naive B-cells, primarily acts as a B-cell receptor (BCR). It's involved in basophil and mast cell activation, and while its full range of functions remains a subject of study, its contribution to the immune system is undeniable.

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FAQs

How are the various cells of the immune system generated, and how do they differentiate from each other?

All cells of the immune system start as hematopoietic stem cells in the bone marrow. These stem cells can differentiate into a variety of immune cells such as granulocytes, monocytes, dendritic cells, and lymphocytes. By responding to various signals and factors, these stem cells can further mature into a variety of specialised immune cells under specific conditions.

What are the functions of granulocytes, such as neutrophils, eosinophils and basophils, in the immune system?

Granulocytes, which include neutrophils, eosinophils and basophils, are part of the innate immune system. Neutrophils are the most abundant white blood cells and they act by phagocytosing, or engulfing, invading pathogens. Eosinophils are primarily involved in combating parasitic infections and also play a role in allergic reactions. Basophils release inflammatory mediators and are involved in the defense against parasites and play a role in allergic reactions as well.

What role do mast cells play in immunology?

Mast cells are involved in the inflammatory response and play a crucial role in the defense against pathogens. They release histamine and other inflammatory mediators upon activation. While they are necessary for immune defense, overactive mast cells can contribute to inflammatory and allergic diseases like asthma and dermatitis.

What role do monocytes, macrophages and dendritic cells play in the immune response?

Monocytes, macrophages and dendritic cells are a group of dedicated antigen-presenting cells. They process and present antigens to T-cells to induce an adaptive immune response. Monocytes circulate in the blood and can differentiate into macrophages or dendritic cells. Macrophages are efficient in engulfing and destroying pathogens, while dendritic cells play a key role in initiating and shaping the adaptive immune response.

What are the different types of lymphocytes and what are their roles in the immune system?

Lymphocytes include natural killer cells, B-cells, and T-cells. Natural killer cells are part of the innate immune system and can kill infected cells without prior exposure. B-cells produce antibodies which can bind to specific antigens and neutralize or flag them for destruction. T-cells are further divided into helper T-cells which assist B-cells and other immune cells, and cytotoxic T-cells which can kill infected cells directly.

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