Immunology is a branch of biology that covers the study of physiological functions of the immune system in vitro, in situ, and in vivo. It deals with the states of both health and disease along with the malfunctions of the immune system in immunological disorders like hypersensitivities, transplant rejection, allergies, immune deficiency, and autoimmune disorders.
Immunology estimates, charts, and examines the body’s system of defense against the infection-causing microorganisms and with disorders in that system’s functioning. It is a healthy and protective mechanism for healthy body derives from word ‘immuis’ means, free from burden.
Immunology also contextualizes the body’s resistance to invasion by other organisms (i.e., immunity). Immunology has a vast array of applications in several disciplines of science and medical science like rheumatology, organ transplantation, parasitology, oncology, virology, bacteriology, psychiatry, and dermatology.
In case, the immune system is not functioning appropriately, it can cause diseases like autoimmunity, allergy and cancer. Research also shows now that immune responses can contribute to the development of many common disorders not commonly considered as immunologic, such as metabolic, cardiovascular, and neurodegenerative conditions like Alzheimer’s.
Why is immunology important?
An innovation that has perhaps saved more precious lives than any other medical advance was from Edward Jenner’s pioneering work in the mid of 18th Century. This ultimately led to vaccination in its modern form. A lot of other scientific breakthroughs in the 19th and 20th centuries lead to the manipulation of amongst other things such as identification of blood groups, safe organ transplantation. In the recent era, immunology has changed the face of modern medicine by predominant usage of monoclonal antibodies throughout science and healthcare.
Immunological research also continues to expand horizons in understanding of how to treat specific health issues along with the ongoing research efforts in autoimmune diseases, vaccines for emerging pathogens, such as Ebola, and immunotherapy. Advancing knowledge of the basic immunology is significant for the clinical and commercial application. To manage a wide array of diseases, discovery of new diagnostics and treatments has facilitated with its help as well. In addition, coupled with advancing modern technologies, immunological research work has provided significantly important research procedures and tools including flow cytometry and antibody technology.
What is immune system?
Immunology primarily covers the immune system which may include immune tissues and organs, immune cells, immune molecules, and tissues to provide non-specific and specific protection against microbial toxins, microorganisms, and tumor cells. Examining its structure and function is crucial to human survival. Immunity refers to the state of protection from infectious disease and immune response is the collective and coordinated response to the introduction of foreign substances. Immune cells communicate with the help of soluble mediators (extracellular, receptor/ligand-specific, paracrine vs endocrine), signal transduction, and direct contact including antigen and cytotoxicity.
The major components of the immune system are cellular in nature and are typically not associated with any certain organ. They are widely present in circulation process throughout the body.
Key lymphoid organs of the immune system
Primary immune organs are involved in the formation and maturation of the immune cells. They include:
- Bone marrow for differentiation and B cell maturation
- Thymus for T cell maturation
- Bursa of Fabricius for the maturation of B cells
Secondary immune organs play roles in the activation of immune cells, such as:
- Lymph nodes
- Mucosa-associated lymphoid tissue
Cells Involved in Immunity
Three main types of cells are involved in immunity:
- B cells
- T cells
Cells involved in immunity are derived from common progenitor cell in bone marrow (Pluripotent hematopoietic stem cell) and progenitor stem cells. Stem cells’ erythroid lineage includes erythrocytes and megakaryocytes, myeloid lineage includes monocyte/macrophage, dendritic cells, PMN’s, mast cells, and lymphoid lineage includes small and large lymphocytes.
These cells circulate in the blood after leaving the bone marrow and survive only a day or so before they enter the tissue to mature into macrophages. They are involved in phagocytosis and intracellular killing of the microorganisms, generation of toxic metabolites through respiratory burst, and the formation of nitric oxide, hydrogen peroxide, superoxide anion.
Monocytes/Macrophages are antigen processing cells which can chew ingested proteins, and degrade enzymes in lysosomal granules. When monocytes enter the tissues, they are called macrophages where they may increase the production of intracellular lysozymes and bring about greater phagocytosis. Macrophages can live in tissue for several years.
Activation of these cells takes place either by the phagocytosis of antigens or in response to the T cell derived cytokines. After activation, they chracterize and remove the unwanted particles secrete cytokines, lysozymes, chemokines, and other factors to regulate the immune response. In chronic inflammation, macrophage scavengers can become giant cells for foamy macrophages.
When macrophages stable in tissues for prolonged periods of time, they carry different morphologies depending on their tissues of residence, such as they are called mesangial cells when present in the kidney, microglial cells in the brain, and Kupﬀer cells in the liver.
The important functions of macrophage include:
- As apcs in T-cell activation
- Effector cells in various forms of cell-mediated immunity
- Serves to eliminate intracellular microbes
- Empowers strong capabilities to kill ingested microbes
- Plays important part in the effector phase of humoral immunity
- Efficiently phagocytose and destroys microbes that are typically coated by igg or c3b
2. B cells
They develop from stem cells present in the bone marrow. B lymphocytes produce antibodies with accuracy for antigens and present it on their surfaces to function as BCRs. They play an integral part in humoral immunity.
B cells form terminally differentiated plasma cells to secrete immunoglobulin. B cells can switch to form a different class of antibody, with the same antigen specificity upon activation. The process of activation into antibody secreting cells depends on antigen.
3. T cells
T lymphocytes are formed in the thymus which are highly specific in cell mediated immunity regulating immune responses. They are also important in the production of B cell-antibody. One of their groups destroys infected cells by inducing apoptosis while the other group secrete cytokines that activate B lymphocytes and phagocytes. Some phagocytes grasp the pathogen and display fragments of its antigens on their surface when pathogens infect tissues. These antigen presenting cells stimulate the production of a T lymphocytes clone that migrates to the site of infection under the direction of cytokines.
T cells provide specific defence as they contain specific surface proteins that allow them to differentiate between the surface molecules of the body’s own cells and cells with foreign molecules on their surface.
Mature T cells with a CD4 marker are known as helper T cells (Th cells) while cells with CD8 marker positive cells are cytotoxic T cells (Tc cells). Different types of T cells perform variety of functions, such as:
- Type 1 helper T cells or TH1 cells reacts with mononuclear phagocytes for the destruction of intracellular pathogens.
- Type 2 helper T cells or TH2 cells interacts with B cells and are significant to divide, differentiate, and make antibody
- Cytotoxic T lymphocytes (CTLs or TC cells) help destruction of the host cells that have become infected by viruses or other intracellular pathogens.
- Regulatory T cells or Tregs play an important role controlling the development of immune responses and limit reactions against self-tissues.
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