Introduction
The immune system is an important system in the human body because it helps in the prevention of infections and the destruction of pathogens. The immune system comprises immune molecules, immune cells, tissues, and organs, which collectively function in the prevention of infections and the destruction of pathogens. Usually, when pathogens enter the body, the immune system recognizes them as antigens, which elicit an immune response (Ohls & Yoder 2008). The ability of the immune system to recognize pathogens as antigens determine the nature of the immune response. An immune response normally entails the production of antibodies that are specific to pathogens recognized by the immune system as antigens. Fundamentally, the immune system of an individual can respond to pathogens using innate immunity or adaptive immunity. Innate immunity is an inherent capacity of the body to provide a nonspecific immune response to different types of antigens. In contrast, adaptive immunity is an acquired immunity that provides an immune respond that is specific to recognized antigens. In this view, this essay examines poliovirus and adaptive immunity that the body acquires against it during vaccination.
Poliovirus
Poliovirus is a virus that a person can acquire immunity against it following immunization. It is an enterovirus (RNA virus), which causes poliomyelitis among children. Poliomyelitis is a paralytic disease because poliovirus enters into the central nervous system and damage motor neurons, thus causing permanent paralysis of limbs. Like other viruses, poliovirus enters into the cells and integrates into DNA, thus becoming part of the host’s genome. After integrating into the host’s genome, poliovirus hijacks the transcription and translation machinery of the cells and replicates using it. According to Grassly, Jafari, Bahl, Durrani, Wenger, Sutter, and Ayward (2009), the Global Polio Eradication Initiative recommends the use of trivalent oral polio vaccine (TOPV) in generating adaptive immunity among children. TOPV consists of live polioviruses that have undergone the attenuation process during their production. The attenuation reduces pathogenicity or the virulence capacity of the poliovirus but maintains its capacity to elicit immune responses in the body. Therefore, during vaccination, the introduction of the attenuated poliovirus triggers a primary immune response and primes the immune system to provide a secondary immune response, which is very effective, in case of a real infection.
Components of Immune Response
The immune response composts leucocytes, antibodies, complement system, interferon, and hormones. During an immune response, antigens triggers production these components in various concentrations as they aid in prevention of diseases and destruction of pathogens. The first component is the leucocytes, which provide cell-mediated immunity because they consist of immune cells. Granulocytes, monocytes, and lymphocytes are three types of leucocytes that help in eradication of pathogens in the body. Antibodies comprise a second component of immune response, as they are immune proteins that leucocytes (plasma cells) produce in response to certain antigens in the body. The common types of antibodies classified according to their structure and functions are immunoglobin A, D, E, M & G (Delves, Martin, Burton, & Roitt 2011). Antibodies fight infections through neutralization of toxins and opsonisation of pathogens.
The complement system is the third component of the immune response. The complement system comprises of diverse proteins that function in a cascade manner when eliciting immune responses in both adaptive and innate immunity. According to Delves, Martin, Burton, and Roitt (2011), the function of the complement system is to enhance immune response by activating leucocytes and antibodies during immune response. The fourth component of the immune response is interferon. The interferon is a protein that enhances cell signalling, prevents infection, and replication of viruses in the cells. The fifth important component of the immune response is the hormones. Lymphokine is an example of hormone that mediates immune responses.
Processing and Presentation of Antigens
The principles of the immune response are that immune cells must process and present antigens on their surfaces to elicit appropriate immune response. For an appropriate and specific immune response to occur, antigen presenting cells such as dendritic cells, B-cells, and macrophages must process and present antigens on their surfaces when complexed with major histocompatibility complexes (MHCs). Depending on the nature of pathogens, antigen-presenting cells can process and present antigens as either MHC II or I proteins (Playfair & Chain 2012). While MHC II presents exogenous proteins, MHC I presents endogenous proteins. In this view, processing of poliovirus proteins occurs through an endogenous pathway while presentation occurs through MHC I. Since poliovirus enters into a cell and integrates its genetic material into cellular genome, it hijacks protein-synthesizing machinery leading to production of viral proteins instead of cellular proteins. Therefore, antigen-presenting cells process viral proteins via endogenous pathway and eventually present them as MHC I.
Activation of Immune Cells and Their Interactions
Activation of the immune cells due to the infection of poliovirus occurs when antigen presenting cells process and present polio proteins as antigens complexed with MHC I. The MHC I plays a central role in activating the immune response when poliovirus invades the cells and causes poliomyelitis. When antigen presenting cells process and present antigens in form of MHC I, immune response occurs. The MHC I activates naive T-cells by presenting antigens in a form that receptors of these cells can recognize. T-cell receptor on the cytotoxic T-cells (CD+8) binds on the viral proteins complexed as MHC I and elicit an immune response (Elgert 2009). The binding T-cell receptor leads to activation of cytotoxic T-cells to release cytokines such as interleukin-2 (IL-2). The IL-2 then causes cascades of immunological reactions that eventually lead to the destruction of cells infected with poliovirus. Cross-presentation of the viral proteins via MHC II proteins activates naive B-cells. The binding of T-helper cells on the MHC II proteins triggers the release of cytokines, which consequently activate proliferation of naive B-cells. Thus, the mature B-cells release antibodies, which aid in the identification and destruction of infected cells in the body.
The interaction of immune cells after activation of immune response entails cascade of immunological events mediated by cells and molecules. When MHC I proteins interact with T-cell receptor on the surface of the T-cell, it stimulates it to differentiate and mature into cytotoxic T-cell. Cytotoxic T-cells then recognize infected cells and destroy them as a way of preventing viral replication. Moreover, cytotoxic T-cell releases IL-2, which enhances differentiation and maturation of cytotoxic T-cells into effector T-cells and memory T-cells (Elgert 2009). The memory T-cells are important as they provide immunity against secondary infections. Comparatively, cross-presentation of viral proteins via MHC II and the release of IL-2 stimulate B-cells to differentiate and mature into plasma cells, which release antibodies. The antibodies combat infected cells by blocking the virus from replicating and infecting other cells. The infection prime plasma cells and make them become memory B-cells, which can readily provide immediate response in case of secondary infection.
Conclusion
The immune system helps the body to eliminate pathogens and prevent infections. The immune system comprises of leucocytes, antibodies, complement system, interferon, and hormones, which collectively play a central role of eliminating pathogens and preventing infections. Poliovirus is an example of a virus that triggers immune response and causes poliomyelitis. Since it is a virus, antigen presenting cells process and present its proteins as MHC I proteins. The MHC activates T-cells and B-cells to provide a specific immune response. Through vaccination, a body acquires adaptive immunity against poliovirus because the oral polio vaccine has attenuated viruses that prime T-cells and B-cells.
References
Delves, P, Martin, S, Burton, D, & Roitt, I 2011, Essential Immunology (12th Ed), Wiley-Blackwell, London.
Elgert, K 2009, Immunology: Understanding the immune system, John Wiley & Sons, London.
Grassly, N, Jafari, H, Bahl, S, Durrani, S, Wenger, J, Sutter, R, & Ayward, B 2009, ‘Mucosal immunity after vaccination with monovalent and trivalent oral poliovirus vaccine in India’, Journal of Infectious Disease, vol. 200 no. 5, pp. 794-801.
Ohls, R, & Yoder, M 2008, Haematology, Immunology, and Infectious Disease: Neonatology Questions and controversies, Elsevier Health Sciences, New York.
Playfair, J, & Chain, B 2012, Immunology at a Glance, John Wiley & Sons, London.