Immunity: refers to a state of acquired or innate resistance or protection from a pathogenic microorganism or its products or from the effect of toxic substances such as snake or insect venom.
Immunology: is that branch of biomedical science concerned with the response of the organism to immunogenic(Antigenic) challenge, the recognition of self from nonself, and all the biological (in vivo), serological (in vitro, physical, and chemical aspects of immune phenomena.
Immune system: is a network of cells, tissues, and organs that work together to defend the body against attacks by “foreign” invaders. These are primarily microbes (germs) tiny, infection-causing organisms such as bacteria, viruses, parasites, and fungi.
Antigen: is a substance or molecule that is recognized by the immune system. An antigen can be a microbe such as a virus, or even a part of a microbe. Tissues or cells from another person (except an identical twin) also carry non self-markers and act as antigens. This explains why tissue transplants may be rejected.
Antibody: is molecule (also called immunoglobulin) produced by a B cell in response to an antigen. When an antibody attaches to an antigen, it helps the body destroy or inactivate the antigen. An antibody is made up of two heavy chains and two light chains. The variable region, which differs from one antibody to the next, allows an antibody to recognize its matching antigen.
Although antibodies can bind to and neutralize bacterial toxins directly, they exert most of their effect by binding to the surface of bacteria, viruses, or other parasites, and thus increasing their adherence to, and phagocytosis by, myeloid cells. This phenomenon is known as opsonization. Antibody also activates complement on the surface of invading pathogens
Lymphoid organs: the organs of the immune system, where lymphocytes develop and congregate. They include the bone marrow, thymus, lymph nodes, spleen, and various other clusters of lymphoid tissue. Blood vessels and lymphatic vessels are also lymphoid organs.
Lymph: a transparent, slightly yellow fluid that carries lymphocytes, bathes the body tissues, and drains into the lymphatic vessels.
Lymph nodes: small bean-shaped organs of the immune system distributed widely throughout the body and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells.
Lymphocytes: small white blood cells produced in the lymphoid organs and paramount in the immune defenses. B cells and T cells are lymphocytes.
Immune responses are categorized as:
Innate immune responses: rapid and immediate host response to entry of a foreign pathogen and usually includes the physical, chemical and microbiological barriers.it do not adapt with repeated exposure to the same pathogen. An example of innate immunity is phagocytic cells (i.e., monocytes, macrophages, and neutrophils), which possess a number of inherently antimicrobial peptides and proteins that kill many different, rather than one specific pathogen.Specific adaptive immune responses will increase after exposure to a pathogen. Lymphocytes (e.g., T-cells and B-cells) are important in the fundamental form of specific adaptive immunity. The ability of T-cells and B-cells to recognize specific oligomeric structures on a pathogen and generate progeny that also recognize the structure enables the immune system to respond more rapidly and effectively when exposed to that pathogen again.
The main cells of the immune system are derived from the lymphoid and myeloid arms of the hematopoietic system.
In the bone marrow, the myeloid arm gives rise to:
Peripheral dendritic cells,
phagocytes (neutrophils and monocytes),
mast cell precursors,
basophils,
eosinophils,
platelets,
Erythrocytes.
In the bone marrow, the lymphoid arm gives rise to:
NK-cells,B-cells,
Pre-T-cells (differentiate to T-cells in the thymus).
In the tissues:
Peripheral dendritic cells,Monocytes (can become a macrophage)
Mast cell precursors further differentiate.
In secondary lymphoid organs, including lymph nodes and the spleen:
They are areas where antigen presenting cells, (B-cells and dendritic cells) present antigen to T-cells.Terminal differentiation of B- and T-cells also occurs in these organs.
Cells of immunity responses:
Cells possess receptors, (which are molecules on the cell surfaces that enable the cell to interact with other molecules or cells.
Receptors reflect and dictate the function of cells. Historically, the names given to receptors often related to function.
Cells of the immune system those are important in inflammation and host defenses include in mast cells, dermal dendrocytes (histiocytes), peripheral dendritic cells, neutrophils, monocytes/macrophages, T-cells, B-cells, and NK-cells.
Other hematopoietic leukocytes (i.e., basophils, eosinophils, erythrocytes, and platelets) also participate in certain forms of inflammation or immune function.
B cell: is a small white blood cell crucial to the immune defenses. Also known as B lymphocytes, they come from bone marrow and develop into blood cells called plasma cells, which are the source of antibodies.
Plasma cells: large antibody-producing cells that develop from B cells.
T cells: small white blood cells (also known as T lymphocytes) that recognize antigen fragments bound to cell surfaces by specialized antibody-like receptors. “T” stands for thymus, where T cells acquire their receptors. There are two types of T cells:
Helper T cell (TH cell): is a subset of T cell that carries the CD4 surface marker and are essential for turning on antibody production, activating cytotoxic T cells, and initiating many other immune functions.
Cytotoxic T lymphocytes, which are the main immunological effector mechanisms involved in the elimination of non-self or infected cells.
Memory cells: a subset of T cells and B cells that have been exposed to antigens and can then respond more readily when the immune system encounters those same antigens again.
3. Antigen-presenting cells, such as the macrophages and macrophage-related cells play a very significant role in the induction stages of the immune response by trapping and presenting both native antigens and antigen fragments in a most favorable way for the recognition by lymphocytes. In addition, these cells also deliver activating signals to lymphocytes engaged in antigen recognition, both in the form of soluble mediators (interleukins such as IL-12 and IL-1) and in the form of signals delivered by cell-cell contact.
4. Phagocytic and cytotoxic cells, such as monocytes, macrophages, and granulocytes, also play significant roles as effectors of the immune response. Once antibody has been secreted by plasma cells and is bound by the microbes, cells, or compounds that triggered the immune response, it is able to induce their ingestion by phagocytic cells. If bound to live cells, antibody may induce the attachment of cytotoxic cells that cause the death of the antibody-coated cell (antibody-dependent cellular cytotoxicity; ADCC). The ingestion of microorganisms or particles coated with antibody is enhanced when an amplification effector system known as complement is activated.
5. Natural killer (NK) cells: large granule-containing lymphocytes play a dual role in the elimination of infected and malignant cells. These cells are unique in that they have two different mechanisms of recognition: they can identify directly virus-infected and malignant cells and cause their destruction, and they can participate in the elimination of antibody-coated cells by ADCC.
Phagocytes: large white blood cells that contribute to the immune defenses by ingesting microbes or other cells and foreign particles.
Phagocytosis: process by which one cell engulfs another cell or large particle.
Monocytes: large phagocytic white blood cells which, when entering tissue, develop into macrophages.
Macrophage: a large and versatile immune cell that devours invading pathogens and other intruders. Macrophages stimulate other immune cells by presenting them with small pieces of the invaders.
Mast cell: a granulocyte found in tissue. The contents of mast cells, along with those of basophils, are responsible for the symptoms of allergy.
Dendritic cells: A rare cell type found in the T cell area of all lymphoid tissues, whose function is to present antigen to T cells, and thus initiate all T cell-dependent immune responses. Not to be confused with follicular dendritic cells, which store antigen for B cells
Basophil: is a white blood cell that contributes to inflammatory reactions. Along with mast cells, basophils are responsible for the symptoms of allergy.
Eosinophil: is a white blood cell that contains granules filled with chemicals damaging to parasites, and enzymes that affect inflammatory reactions.
Complement: is a complex series of blood proteins whose action “complements” the work of antibodies. Complement destroys bacteria, produces inflammation, and regulates immune reactions.
Immunoglobulin: is a family of large protein molecules, also known as antibodies, produced by B cells.
Cytokines: is a powerful chemical substances secreted by cells that enable the body’s cells to communicate with one another. Cytokines include lymphokines produced by lymphocytes and monokines produced by monocytes and macrophages.