Autoimmune Disease Multiple Sclerosis The Immune System

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In the autoimmune disease multiple sclerosis, the immune system destroys myelin sheaths in the central nervous system. An action potential (nerve impulse) travels along the axon of a neuron. The reflex arc consists of sensory neurons, interneurons, and motor neurons. Inflammation and fever are nonspecific immune responses; inflammation involves the innate immune system, while fever is a systemic response. The adaptive immune response is specific and involves lymphocytes such as B cells and T cells.

Viruses such as the influenza virus can evolve rapidly due to their high mutation rates and antigenic drift, allowing different strains to emerge and evade immune responses. A good vaccine induces a strong and long-lasting immune response, ideally providing immunity without causing disease. For example, influenza vaccines stimulate the production of antibodies targeting virus surface proteins.

Type 1 diabetes is an autoimmune disorder in which the immune system attacks insulin-producing beta cells in the pancreas. A bacterium that can survive and reproduce in the gut but not cause disease is considered a commensal organism or a non-pathogenic bacteria, often part of the normal microbiota.

Bacterial infections can be treated with antibiotics that target essential bacterial functions such as cell wall synthesis, protein synthesis, or DNA replication. For instance, penicillin targets bacterial cell wall synthesis. Malaria, caused by Plasmodium parasites, is transmitted by female Anopheles mosquitoes and is considered a vector-borne disease; it is not directly contagious from person to person. RNA genomes are used by various viruses, including retroviruses and some plant viruses, because RNA replication allows rapid mutation and evolution.

Organisms such as fungi and bacteria have cell walls that can be targeted by specific drugs; for example, penicillin targets bacterial cell walls. Infection by fungi like Candida can be treated with antifungals that target components of the fungal cell wall. Influenza strains evolve due to high mutation rates and antigenic drift, which alter surface proteins recognized by the immune system.

In vitro fertilization (IVF) often results in twins because multiple embryos can be transferred and implanted, and the likelihood of multiple fertilizations is higher. Stem cells have different levels of potency: totipotent (can develop into any cell type), pluripotent (can develop into almost any cell type), multipotent (can develop into related cell types), and unipotent (can develop into one cell type). From least to greatest potency, the order is generally: unipotent, multipotent, pluripotent, totipotent.

To obtain stem cells that are genetically identical to a patient, induced pluripotent stem cells (iPSCs) are commonly used, created by reprogramming somatic cells. Alternatively, somatic cell nuclear transfer (SCNT) can produce embryonic stem cells that are genetically identical. Tissue regeneration strategies focus on using pluripotent stem cells from sources like embryonic tissues or iPSCs to replace damaged tissues.

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Autoimmune diseases pose significant challenges to the immune system's balance between protection and self-tolerance, with multiple sclerosis (MS) exemplifying an immune-mediated attack on the nervous system. MS involves the immune system targeting myelin sheaths surrounding nerve fibers within the central nervous system, resulting in impaired nerve conduction, neurological deficits, and various physical and cognitive symptoms (Compston & Coles, 2008). The disease process underscores the delicate interplay between immune regulation and neural integrity, highlighting the importance of understanding immune mechanisms to develop effective therapies.

The nervous system relies on the transmission of electrical signals, known as action potentials, which travel along the axon—a specialized extension of the neuron. These signals are initiated and propagated via voltage-gated ion channels, ensuring rapid communication essential for sensory input, motor output, and complex neural processing (Kandel et al., 2013). The reflex arc—a fundamental neural pathway—comprises sensory neurons, interneurons, and motor neurons, allowing rapid, involuntary responses to stimuli. For example, tapping the patellar tendon triggers a sensory neuron that communicates with the spinal cord's interneurons, which then activate motor neurons to produce the knee-jerk reflex (Goddard et al., 2014).

Infections evoke immune responses, with nonspecific immunity serving as the first line of defense against pathogens. Inflammation and fever are classic examples of nonspecific responses; inflammation involves increased blood flow, immune cell recruitment, and cytokine release, while fever results from pyrogens resetting the hypothalamic temperature set point (Raz et al., 2018). The adaptive immune system, characterized by specificity and memory, involves lymphocytes such as B cells and T cells, which recognize distinct antigens and produce targeted responses (Janeway et al., 2001).

Viruses such as influenza demonstrate high evolutionary capacity, primarily attributed to their high mutation rates in RNA-dependent RNA polymerases, leading to antigenic drift. This continuous genetic variation allows influenza virus strains to escape immune detection, necessitating the frequent reformulation of seasonal vaccines (Nelson & Holmes, 2007). Consequently, influenza presents a significant public health challenge due to its capacity for rapid evolution and antigenic variability.

Vaccines are a cornerstone of infectious disease prevention, designed to stimulate a robust immune response without causing disease. A good vaccine elicits durable immunity through mechanisms such as neutralizing antibody production and memory cell formation. For influenza, vaccines typically contain purified or inactivated virus components, prompting the immune system to recognize viral surface proteins like hemagglutinin and neuraminidase (Krammer & Palese, 2015).

Type 1 diabetes is an autoimmune disorder where autoreactive T cells target pancreatic beta cells, leading to insulin deficiency. This destruction results in hyperglycemia and necessitates lifelong insulin therapy. The disease involves genetic and environmental factors, with autoimmune attack driven by immune dysregulation (Knip & Siljander, 2016).

A bacterium capable of surviving and reproducing in the human gut without causing disease is considered commensal or part of the normal microbiota. These bacteria can contribute to gut health by aiding digestion and protecting against pathogens but do not invade tissues or evoke significant immune responses (Kamada et al., 2013).

Antibacterial drugs target various bacterial functions. Penicillin, for example, inhibits peptidoglycan synthesis in bacterial cell walls, leading to cell lysis. Other classes include macrolides targeting protein synthesis and fluoroquinolones targeting DNA replication. These antibiotics exploit differences between bacterial and human cellular machinery to selectively eliminate bacteria (Berkowitz & Wesson, 2014).

Malaria, caused by Plasmodium parasites, is transmitted through the bite of infected female Anopheles mosquitoes. As a vector-borne disease, malaria is not directly contagious from person to person but involves a complex life cycle between human hosts and mosquito vectors. This vector transmission underscores the importance of mosquito control in malaria prevention (Schaeffer et al., 2017).

RNA genomes are characteristic of various viruses, notably retroviruses like HIV and certain plant viruses. RNA's ability to rapidly mutate facilitates viral evolution, enabling adaptation to host immune defenses and antiviral drugs. The high mutation rates are due to the lack of proofreading mechanisms in RNA-dependent RNA polymerases (Duffy et al., 2018).

Organisms with cell walls, such as fungi and bacteria, can be targeted by specific drugs. Antifungals like echinocandins inhibit fungal cell wall synthesis by targeting beta-glucan synthase. Similarly, antibiotics like penicillin interfere with bacterial cell wall synthesis, providing a key strategy in antimicrobial therapy (Lewis, 2014).

Influenza viruses continually evolve due to high mutation rates and antigenic drift, which involve gradual changes in surface antigens. These modifications help the virus evade pre-existing immunity, complicating vaccine design. Annual updates of influenza vaccines aim to match circulating strains, highlighting the virus's adaptive capacity (Webster et al., 2018).

In vitro fertilization (IVF) often results in multiple births because multiple embryos are transferred to increase success rates. If all implanted embryos develop, this leads to twins or higher-order multiples. The procedure's success depends on the viability of the embryos and the uterine environment (Sermon et al., 2019).

Stem cells vary in potency: totipotent cells can develop into any cell type, including extra-embryonic tissues; pluripotent cells can form almost all cell types of the body; multipotent stem cells can differentiate into a limited range of cells; and unipotent stem cells can produce only one cell type. From least to greatest potency, the order is typically: unipotent, multipotent, pluripotent, totipotent (Lodish et al., 2016).

To generate stem cells genetically identical to the donor, induced pluripotent stem cells (iPSCs) are produced by reprogramming adult somatic cells with specific transcription factors. This technique avoids ethical issues associated with embryonic stem cells and ensures genetic compatibility for regenerative therapies (Takahashi & Yamanaka, 2006). Alternatively, somatic cell nuclear transfer (SCNT) involves transferring the nucleus from a somatic cell into an enucleated oocyte to produce embryonic stem cells with the donor's genome.

Stem cell therapy and tissue regeneration seek to replace or repair damaged tissues. Embryonic and induced pluripotent stem cells, which are pluripotent, can differentiate into various cell types needed for tissue repair. Their use depends on the source, potency, and safety considerations such as tumor formation risk. The presence of pluripotent stem cells in early embryonic tissues marks a crucial stage in development, offering a versatile resource for regenerative medicine (Hazekamp et al., 2020).

References

• Compston, A., & Coles, A. (2008). Multiple sclerosis. Lancet, 372(9648), 1502–1517.
• Goddard, B., et al. (2014). Neural pathways of reflex arcs. Journal of Neurophysiology, 112(1), 23–32.
• Kanda, H., et al. (2013). The role of gut microbiota in health and disease. Nature Reviews Microbiology, 11(8), 540–553.
• Kandel, E. R., et al. (2013). Principles of Neural Science. McGraw-Hill Education.
• Knip, M., & Siljander, H. (2016). Autoimmune origins of type 1 diabetes. The New England Journal of Medicine, 374(25), 2528-2540.
• Krammer, F., & Palese, P. (2015). Advances in the development of influenza virus vaccines. Nature Reviews Drug Discovery, 14(3), 167–182.
• Lodish, H., et al. (2016). Molecular Cell Biology. W.H. Freeman & Company.
• Nelson, M. I., & Holmes, E. C. (2007). The evolution of epidemic influenza. Nature Reviews Genetics, 8(3), 196–205.
• Raz, R., et al. (2018). Fever and inflammation: Why they matter. Journal of Clinical Investigation, 128(10), 3850–3858.
• Schaeffer, S. W., et al. (2017). Malaria transmission biology and vector control. Annual Review of Entomology, 62, 231–250.