By Anahita Chauhan & Janhavi Balaji
Abstract
This article will discuss the connection between viruses and the immune system and how this affects the body. There are a few major responses from the Immune system to viruses that are Cellular Immune Response, Adaptive Immune Response, Innate Immune Response, Humoral Immune Response and Memory Immune Response. The initial line of defense against viral infections is the innate immune system. When the innate immune response is not enough to contain the infection, the adaptive immune system kicks in. Lymphocytes are used by the cellular immune response to eradicate the virus. The antibodies that agglutinate the virus to stop it from infecting cells further are part of the hormonal response. The term "memory immune response" refers to the immune cells' ability to retain information about the virus and produce antibodies more quickly in the event of a recurrence.
Aim: The aim of this article is to investigate the interactions between viruses and the immune system, with a specific focus on the functional consequences of the interactions.
Introduction
Viruses are infectious agents made up of a little more than genes enclosed in a protein sheath. They often lack the structures and metabolic machinery seen in cells. Viruses can cause a wide variety of diseases, hence in the late 1800s they were often seen parallel with bacteria and were also called the simplest of living forms. However due to their inability to carry out metabolic activities outside of a host cell they were often questioned of being living or not. Hence, a simple phrase used by two researchers describe viruses to lead “a kind of borrowed life”. The Immune system safeguards the host organism from viruses, bacteria, pathogens and other virus-like organisms. Upon detecting a foreign organism (viruses, pathogens) as a threat it triggers a series of complex processes through detailed communication pathways and effective mechanisms (whose primary purpose is to neutralize and remove the threat). The immune system is a biological “defense mechanism” that can adapt to new threats and can develop memory for faster responses against the same. Its capacity of learning and memorizing patterns of viruses and pathogens, as well as protecting the host organism from threats is what makes it so ‘unique’.
Body
The immune system responds to viruses through a complex procedure. Initially, the innate immune system cells detect the presence of viruses by recognising specific molecular patterns associated with them.
Innate Immune Response
This is done with the help of receptors known as Pathogen-Associated Molecular Patterns (PAMPs). Toll-like receptors are an important class of receptors that are engaged in this detection process (TLRs). Viral components such as viral proteins or nucleic acids (DNA or RNA) can be recognized by TLRs. The innate immune response is triggered by a signaling cascade that is started when a TLR attaches to a viral PAMP. Which involves the synthesis of signaling molecules to draw more immune cells to the infection site.
Adaptive Immune Response
Specific antigens are used by the adaptive immune system, also known as acquired immunity, to deliberately elicit an immunological response. Compared to the innate immune response, which is always primed and prepared to fight, the adaptive immune response reacts to threats and diseases far more slowly. The adaptive immune system, in contrast to the innate immune system, depends only on B cells and T cells to perform their functions. Multipotent hematopoietic stem cells, which are special types of stem cells found in the bone marrow, are the source of both B and T cells, which are lymphocytes. Each B cell possesses one of the millions of unique surface antigen-specific receptors that are included into the DNA of the organism. B Cells Modify Their Nuclear Morphology to Promote Antigen Extraction and Organize the Immune Synapse. T cell receptors can only identify antigens that are attached to specific receptor molecules, known as Major Histocompatibility Complex classes 1 and 2 (MHCI), in contrast to antibodies, which may connect to antigens directly (MHCI). Given that they are necessary for nearly all adaptive immune responses, helper T cells are perhaps the most significant cells in adaptive immunity. They assist in the activation of cytotoxic T cells, which kill infected target cells, as well as B cells, which make antibodies and macrophages, which eliminate ingested microorganisms.
Cellular Immune Response
The Cellular Immune Response, also known as cell-mediated immunity, involves the activation and participation of specialized immune cells to directly combat infections, particularly viral infections. Two crucial types of cells central to this response are Cytotoxic T Lymphocytes (CTLs) and Helper T Cells (TH cells).
1. Cytotoxic T Lymphocytes (CTLs): CTLs play a pivotal role in directly destroying infected host cells. They recognize and bind to cells that display viral antigens on their surface, indicating that the cell is infected. Once activated, CTLs release cytotoxic molecules, such as perforin and granzymes, which create pores in the infected cell's membrane and induce programmed cell death (apoptosis). This process prevents the virus from spreading to other cells.
2. Helper T Cells (TH cells): TH cells are crucial coordinators of the immune response. They assist other immune cells by releasing signaling molecules (cytokines) that regulate the activities of various immune cells.
- Types:
- TH1 cells: Activate and enhance the activity of CTLs, promoting their cytotoxic functions.
- TH2 cells: Stimulate B cells to produce antibodies, which are essential for the elimination of extracellular pathogens.
Functional Consequences:
CTL-Mediated Destruction: The Cytotoxic T Lymphocytes (CTLs) prevent the spread of intracellular pathogens by destroying infected cells
Coordination by Helper T Cells: TH cells regulate the intensity of the response and coordinate the immune system’s responses by activating other immune cells
Humoral Immune Response
B cells are the main source of antigen-specific antibodies produced by humoral immunity. On the other hand, mature T cells, macrophages, and the production of cytokines in response to an antigen are the main drivers of cell-mediated immunity, which is an adaptive immune response that does not rely on antibodies.
Cytopathic effects are the alterations in cell morphology brought on by an infecting virus (CPE). The rounding of the infected cell, the formation of cytoplasmic or nuclear inclusion bodies, and the union of neighboring cells to create a syncytia (polykaryocytes) are typical instances. Either changed host cell architecture or viral component accumulations can be represented by inclusion bodies. Viral interactions with cell membranes have the potential to modify the physiological characteristics of infected cells, such as ion transport, secondary messenger synthesis, and activation cascades that result in modified cellular activity.
Functional Consequences:
Neutralization: Antibodies can neutralize toxins or block the entry of pathogens into host cells.
Opsonization: Antibodies facilitate the recognition and phagocytosis of pathogens by immune cells.
Complement Activation: Antibodies trigger the complement system, enhancing the immune response against pathogens.
Conclusion
To conclude, viruses are infectious organisms with minimal structures and metabolic machinery. The immune system responds to viruses through a complex procedure triggered by receptors known as Pathogen-Associated Molecular Patterns (PAMPs). The immune system however, protects the host organism from viruses through a complex procedure which recognises the specific molecular patterns which helps the immune system neutralize and protects the organism acting as a biological defense mechanism that can actively adapt to new threats as well as develop memory for faster responses.
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