The immune system provides an organism with natural protection against diseases caused by pathogens such as bacteria and viruses and tumor or cancer cells through specific immune responses. To understand further the importance of immune response, it is worth mentioning that a compromised immune system, such as in the case of AIDS caused by unmanaged HIV infection and other conditions associated with immunosuppression, could lead to the development of infection-based diseases and the proliferation of cancer cells.
Complex biological structures and processes characterize the overall mechanism behind the immune system. However, in the simplest illustration, it works through a so-called layered defense based on the two major immune system components: the innate immune system and the adaptive immune system.
Innate vs. Adaptive: The Two Layers of Defense Based on the Major Components of the Immune System
1. Innate Immune Response Based on the Innate Immune System
The innate immune system is a component of the immune system found in all organisms. Considered as an older evolutionary immune strategy and also known as general immune response, it provides the dominant immune response or defense for plants, fungi, primitive multicellular organisms, and insects, as well as for all other vertebrates. Compared to the adaptive immune system, it is not specific and does not confer long-lasting immunity against a pathogen.
Several subcomponents constitute the innate immune system and provide an innate immune response. Take note of the following:
• Surface Barriers: Mechanical, chemical, and biological barriers immediately protect organisms from pathogenic invasion and infection. Examples of these are the waxy cuticles that cover the epidermis of leaves, the exoskeleton of insects, and the skin of most vertebrates.
Biological byproducts from biological processes also provide protections. These include coughing and sneezing for expelling pathogens and irritants from the respiratory tract, saliva and tears for providing antibacterial activities, and gastric acid and proteases for killing ingested pathogens.
• Inflammation: An inflammation is an immune response to harmful stimuli caused by pathogens, irritants, and damaged cells. Its primary function is to remove the cause of cellular or tissue injury through the action of immune cells, clear out cells and damaged tissues, and initiate tissue repair.
Injured and infected cells release the signaling molecules eicosanoids and cytokines to induce the inflammatory process. These signaling molecules raise body temperature, dilate blood vessels, attract or recruit immune cells, and promote healing. Common symptoms of inflammation are redness, swelling, heat, and pain.
• Complement System: The complement system is a set of plasma proteins circulating in the blood and tissue fluids. Most of these proteins are normally inactive. However, infection by a pathogen or a pathogen-bound antibody activates these proteins that in turn, result in an innate immune response. Note that this system also complements the adaptive immune response.
Many organisms, including some invertebrates, fish, and plants have complement systems. In mammals, including humans, the activation of the system or the involved proteins result in the stimulation of immune cells called phagocytes, triggering of a series of inflammatory responses, and the activation of cell-killing membrane attack complex.
• Cellular Barriers: The innate immune system has a class of immune cells called white blood cells or innate leukocytes that act like an independent single-celled organism that identify and eliminate pathogens, regulate the inflammatory response, and activate the adaptive immune system.
Specific types of innate leukocytes include the phagocytes such as the macrophages, neutrophils, and dendritic cells that engulf pathogens, foreign particles, and dead or terminal cells; innate lymphoid cells that contribute to early immune response; mast cells and basophils that regulate inflammatory responses in relation to allergies; eosinophils that combat multicellular parasites and certain infections, and natural killer cells that destroy compromised host cells and cancer cells.
2. Adaptive Immune Response Based on the Adaptive Immune System
The adaptive immune system or the acquired immune system is the second component of the immune system found only in vertebrates. This system evolved in early vertebrates and has since provided a stronger immune response or defense that includes immunological memory that provides an organism with long-lasting immunity against pathogens. Nonetheless, it is called into action against pathogens or abnormal cells that can evade or overcome innate immune response.
In contrast to the innate leukocytes of the innate immune system, the adaptive immune system has the so-called adaptive leukocytes specifically called as lymphocytes. Furthermore, there are two major subtypes of lymphocytes that also correspond to the two components of the adaptive immune system. These are B cells that play a central role in the humoral component of the adaptive immune response and the T cells that play a primary role in the cell-mediated immunity component of the adaptive immune response.
Take note that the innate immune system generally has the humoral immunity and cell-mediated immunity components as well. In the case of the adaptive immune system, humoral immunity involves the activities of the B cells while cell-mediated immunity involves the activities of the T cells. The following are the difference between humoral adaptive immune response and cell-mediated adaptive immunity response:
• Humoral Immunity: This component of the adaptive immune response is concerned with humors or cell-free body fluids and serum. It involves the production of antibody and the initiation of antibody response. Take note that the antibody responses center on the activation of the lymphocyte cells called the B cells to release antibodies or proteins that render pathogenic bacteria and viruses unable to function through binding.
• Cell-Mediated Immunity: This component of the adaptive immune response is concerned with the protective function of immunization associated with cells. Unlike humoral immunity, it does not involve the activation of antibodies. Instead, it involves the activation of T cells. In the specific context of adaptive immunity, cell-mediated immunity also involves immune regulation, elimination of pathogen, and immunological memory.
It is important to reiterate the fact that adaptive immunity provides a stronger immune response and defense than innate immunity. The system confers an organism with an ability to adapt to pathogens, thereby allowing its immune system to mount stronger attack whenever it reencounters similar pathogens.