Antibodies, also known as immunoglobulins, are crucial proteins produced by the immune system. They play a vital role in combating pathogens. When it comes to pathology, IgM antibodies are significant in disease conditions like infections, autoimmunity, and tumors. IgM antibodies are among the five classes of immunoglobulins which also include IgG, IgA, IgE, and IgD. All these classes contribute to safeguarding the body against bacteria, viruses, and other foreign substances. Research suggests that serum IgM antibodies, mainly composed of natural IgM antibodies, are essential in protecting target tissues from immune attacks. Moreover, these antibodies could potentially aid in tissue repair as well.
Fig.1 IgM fights infections and non-communicable diseases.1
IgM Antibodies in Complement Activation
Natural IgM antibodies form immune complexes with antigens and activate complement. IgM antibodies bind to complement receptors on the surface of apoptotic cells or macrophages via their Fc portion. This allows C1q to bind to the Fc portion of the IgM antibody and activate the classical complement pathway by binding to the C1q receptor, which subsequently works synergistically with activated C1q to clear bacterial infections, neutralize viral particles, and clear dead cells, thereby preventing certain bacterial infections. Thus, complement activation also plays an important role in the natural immune response. To enhance the antibody response, IgM antibodies bind to antigen and activate C1q, leading to the deposition of complement on the antigen. The antigen-complement complex then cross-links with the B-cell receptor, which then forms a complement receptor 2 (CR2)/CD19/target of the antiproliferative antibody-1 (TAPA-1) coreceptor complex on the B-cell, thereby lowering the threshold for B-cell activation. In addition, marginal zone B cells bind to IgM-antigen complexes via Fc receptors and are trapped in the marginal zone in mice lacking C3 and CR1/2, causing them to move toward follicular dendritic cells (DCs). In addition, CR1/2 on follicular DCs promotes migration of complement-encapsulated antigen to follicular DCs. Antigen transfer to follicular DCs plays a crucial role in inducing an optimal antibody response.
IgM Antibodies in Immune Responses via the FcµR
The IgM receptor (FcμR) binds to IgM through its Fc portion, which is expressed on the surface of B cells, regulatory T cells, NK cells, granulocytes, macrophages, and dendritic cells. Binding of IgM antibodies to the FcμR inhibits the expression of IgM-BCR on the surface of B cells or regulates T cell and dendritic cell function. IgM antibodies are involved in regulating the elimination of autoantigens and the suppression of autoimmune responses. In addition, IgM antibodies can directly bind to tumor-associated antigens and promote tumor elimination by directly presenting tumor antigens to NK cells and dendritic cells. Therefore, detection of IgM antibodies is considered a promising approach in the early diagnosis and prognostic assessment of tumors. In addition, therapeutic approaches by enrichment of IgM antibodies, which have anti-inflammatory effects and inhibit complement activation and IgG autoantibody production, have been used in clinical practice. In conclusion, IgM antibodies play an important regulatory role in the immune response through their interaction with FcμR.
Overall, IgM antibodies play a crucial role in the body's immune response. It responds promptly to the invasion of pathogens, activates the defense mechanisms of the complement system, and helps to remove pathogens from the body. In pathology, the measurement and analysis of IgM antibody provides an important basis for the diagnosis and treatment of many diseases. As a global professional antibody production supplier, Creative Biolabs has established an advanced non-IgG antibody research platform to provide non-IgG therapeutic antibody development services and high-quality non-IgG antibody products for global customers. If you have any related needs, please feel free to contact us.
Reference
- Jones, Katelyn, et al. "Immunoglobulin M in health and diseases: how far have we come and what next?." Frontiers in Immunology 11 (2020): 595535.
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