Immune response

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The Immune response is the body's response caused by its immune system being activated by antigens. The immune response can include immunity to pathogenic microorganisms and its products, allergies, graft rejections, as well as autoimmunity to self-antigens. In this process the main cells involved are T cells and B cells (sub-types of lymphocytes), and macrophages (a type of leucocyte or white blood cell). These cells produce lymphokines that influence the other host cells' activities. B cells, when activated by helper T cells undergo clonal expansion. B cells differentiate into effector B cells, which are short lived and secrete antibodies, and memory B cells, which are long lived and produce a fast, remembered response when exposed to the same infection in the future. B cells mature to produce immunoglobulins (also known as antibodies), that react with antigens. At the same time, macrophages process the antigens into immunogenic units which stimulate B lymphocytes to differentiate into antibody-secreting plasma cells, stimulating the T cells to release lymphokines. [1]

Immune system A biological system that protects an organism against disease

The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease. To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism's own healthy tissue. In many species, the immune system can be classified into subsystems, such as the innate immune system versus the adaptive immune system, or humoral immunity versus cell-mediated immunity. In humans, the blood–brain barrier, blood–cerebrospinal fluid barrier, and similar fluid–brain barriers separate the peripheral immune system from the neuroimmune system, which protects the brain.

Antigen molecule capable of inducing an immune response (to produce an antibody) in the host organism

In immunology, antigens (Ag) are structures specifically bound by antibodies (Ab) or a cell surface version of Ab ~ B cell antigen receptor (BCR). The terms antigen originally described a structural molecule that binds specifically to an antibody only in the form of native antigen. It was expanded later to refer to any molecule or a linear molecular fragment after processing the native antigen that can be recognized by T-cell receptor (TCR). BCR and TCR are both highly variable antigen receptors diversified by somatic V(D)J recombination. Both T cells and B cells are cellular components of adaptive immunity. The Ag abbreviation stands for an antibody generator.

In biology, immunity is the balanced state of multicellular organisms having adequate biological defenses to fight infection, disease, or other unwanted biological invasion, while having adequate tolerance to avoid allergy, and autoimmune diseases.


Complement is a group of normal serum proteins that enhance the immune response by becoming activated as the result of antigen-antibody interaction. The first contact with any antigen sensitize individual affected and promote the primary immune response. Next of the sensitized individuals with same antigen result in a more rapid and massive reaction, called the secondary immune response ("booster response" or the "anamnestic reaction"). It is most expressed in the level of circulating serum antibodies. [2] [3]

Complement system part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promotes inflammation, and attacks the pathogens cell membrane

The complement system is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promotes inflammation, and attacks the pathogen's cell membrane. It is part of the innate immune system, which is not adaptable and does not change during an individual's lifetime. The complement system can, however, be recruited and brought into action by antibodies generated by the adaptive immune system.

An anamnestic response in medicine is a delayed immunologic response. The term is frequently used in transfusion medicine and refers to a re-exposure incident where antibody is formed on initial exposure to an antigen in a transfused unit, but the specific memory B cell population fades over time, with antibody becoming undetectable over years. If a patient is re-exposed to the same offending antigen in a future transfusion (which might happen because the antibody screen would in fact be negative), there would still be a massive, rapid production of IgG antibody against the antigen, which will predictably lyse the transfused red cells, a delayed hemolytic transfusion reaction.[ citation needed ]

A delayed hemolytic transfusion reaction (DHTR) is a type of transfusion reaction. According to the Centers for Disease Control's (CDC) National Healthcare Safety Network's (NHSN) Hemovigilance Module, it is defined as:

Drawing of a primary immune response with B-cells and T-cells Drawing of Primary Immune Response.svg
Drawing of a primary immune response with B-cells and T-cells

The immune response can be transferred via serum antibodies introduction from sensitized to desensitized individuals. It is highly specific for given antigen, and it is normally directed against foreign protein substances. [2]


Innate response is the first line of defense when it comes to defending an organism from an foreign invader. Foreign invaders include bacteria, viruses, and parasites. The protection an innate response offers is beneficial because it attacks all foreign invaders that are not part of the cell’s self.


An immune response can usually be described generally as "The reaction of the host's immune system to antigen in an invading (infecting) pathogenic organism, or to foreign protein, as in transplanted organs or tissues. The response is humoral and local; antibod[ies] produced by B cells combine... with antigen in an antigen-antibody complex to inactivate or neutralize antigen. This defensive mechanism often effectively controls infection." [4] An immune response is divided into 2 parts; innate and adaptive.

The innate immune response is "the response by the host that comprises the cells and mechanisms that defend the host from infection by other organisms or is activated by endogenous molecules, in a nonspecific manner." [5] The innate immune response is quick and is the body's initial response to unwanted invaders. It consists of the body's non-specific external and internal defense mechanisms. An example of the body's external defense mechanisms are mucus and skin. Skin consists of epithelial and endothelial cells which acts a sort of barrier against infection, invading antigens would have to pass through the initial skin barrier in order to actually get inside the host. Mucous acts similarly to skin, in that it is a barrier of sorts. Mucus traps invading pathogens and sometimes degrades them, preventing them from going any further into the body. Non-specific internal defense mechanisms are put in place in case the invading pathogens gets past the external defenses and actually makes it inside the body. Things such as phagocytes, and Natural Killer (NK) cells attack the pathogen and destroys it before further infection takes place.

The adaptive immune response is the body's second line of defense."Adaptive immunity has evolved to provide a broader and more finely tuned repertoire of recognition for both self- and nonself-antigens. Adaptive immunity involves a tightly regulated interplay between antigen-presenting cells and T and B lymphocytes, which facilitate pathogen-specific immunologic effector pathways, generation of immunologic memory, and regulation of host immune homeostasis." [6] The cells of the adaptive immune system are extremely specific, because during early developmental stages the B and T cells develop antigen receptors that are specific to only certain antigens. This is extremely important for B and T-cell activation. B and T cells are extremely dangerous cells, if they are able to attack without going through a rigorous process of activation, a faulty B or T cell can begin exterminating the host's own healthy cells. Every B and T-cell is different, making way for a diverse community of cells ready to recognize and attack a full range of invaders. This response is much slower than the body's innate response because its cells are so specific and require to be activated before it is able actually act. "In addition to specificity, another principal feature of adaptive immunity is the generation of immunologic memory. During the first encounter with an antigen (pathogen), sets of long-lived memory T and B cells are established. In subsequent encounters with the same pathogen, the memory cells are quickly activated to yield a more rapid and robust protective response". [6] This feature of the adaptive immune response is responsible for the development of vaccines as well as other modern day medicines targeted at disease prevention. Immunologic memory is the basic concept behind the modern day flu shot. The flu shot basically is giving the recipient a dormant flu virus. This activates the recipient's immune response. After the immune response, immunologic memory is activated, so if the individual ever comes into contact with the flu virus again the body will be prepared to deal with it accordingly, this time faster, and more efficiently.

Natural killer cells

NK cells attack self cells that have become infected rather than attack foreign invaders. NK cells have cytotoxic chemicals in which recognize a broad spectrum of foreign invaders which is non-specific. NK cells are bound to foreign substances and insert their cytotoxic chemical which results in the foreign cells to die. NK cells are a type of lymphocyte. In an organism, B and T lymphocytes are present. They grow in the bone marrow and in the liver and produce hematopoetic stem cells. [7]

Natural killer T cells (NKT)

Natural killer T cells are a branch of T cells and a lymphocyte that is involved in the innate response. NKT cells can pinpoint nonpeptide antigens using MHC molecules from CD1 on the cell surface. NKT constantly express T-cell and NK cell antigens.  Invariant NKT cells express a unique TCRa rearrangement, Va24-Ja18 with Vb11 that is expressed that characterizes many NKT cells. When NKT cells are activated, cytokines are rapidly produced. IL-4 is associated in allergy pathogenesis. [6] Ulcerative colitis, UC, is a form of inflammatory bowel disease. Natural killer T cells can play a key role in the disease. According to a recent study, by manipulating natural killer T cells, we can modify abnormal immunoresponse activity in UC. [8]

Related Research Articles

Natural killer cells, or NK cells, are a type of cytotoxic lymphocyte critical to the innate immune system. The role NK cells play is analogous to that of cytotoxic T cells in the vertebrate adaptive immune response. NK cells provide rapid responses to virus-infected cells, acting at around 3 days after infection, and respond to tumor formation. Typically, immune cells detect major histocompatibility complex (MHC) presented on infected cell surfaces, triggering cytokine release, causing lysis or apoptosis. NK cells are unique, however, as they have the ability to recognize stressed cells in the absence of antibodies and MHC, allowing for a much faster immune reaction. They were named "natural killers" because of the initial notion that they do not require activation to kill cells that are missing "self" markers of MHC class 1. This role is especially important because harmful cells that are missing MHC I markers cannot be detected and destroyed by other immune cells, such as T lymphocyte cells.

Lymphocyte Subtype of white blood cell

A lymphocyte is one of the subtypes of a white blood cell in a vertebrate's immune system. Lymphocytes include natural killer cells, T cells, and B cells. They are the main type of cell found in lymph, which prompted the name "lymphocyte".

Humoral immunity or humoural immunity is the aspect of immunity that is mediated by macromolecules found in extracellular fluids such as secreted antibodies, complement proteins, and certain antimicrobial peptides. Humoral immunity is so named because it involves substances found in the humors, or body fluids. It contrasts with cell-mediated immunity. Its aspects involving antibodies are often called antibody-mediated immunity.

Cell-mediated immunity is an immune response that does not involve antibodies, but rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. Historically, the immune system was separated into two branches: humoral immunity, for which the protective function of immunization could be found in the humor and cellular immunity, for which the protective function of immunization was associated with cells. CD4 cells or helper T cells provide protection against different pathogens. Naive T cells, mature T cells that have yet to encounter an antigen, are converted into activated effector T cells after encountering antigen-presenting cells (APCs). These APCs, such as macrophages, dendritic cells, and B cells in some circumstances, load antigenic peptides onto the MHC of the cell, in turn presenting the peptide to receptors on T cells. The most important of these APCs are highly specialized dendritic cells; conceivably operating solely to ingest and present antigens.

Adaptive immune system subsystem of the overall immune system that is composed of highly specialized, systemic cells and processes that eliminate pathogens or prevent their growth

The adaptive immune system, also known as the acquired immune system or, more rarely, as the specific immune system, is a subsystem of the overall immune system that is composed of highly specialized, systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system is one of the two main immunity strategies found in vertebrates. Acquired immunity creates immunological memory after an initial response to a specific pathogen, and leads to an enhanced response to subsequent encounters with that pathogen. This process of acquired immunity is the basis of vaccination. Like the innate system, the acquired system includes both humoral immunity components and cell-mediated immunity components.

Alloimmunity is an immune response to nonself antigens from members of the same species, which are called alloantigens or isoantigens. Two major types of alloantigens are blood group antigens and histocompatibility antigens. In alloimmunity, the body creates antibodies against the alloantigens, attacking transfused blood, allotransplanted tissue, and even the fetus in some cases. Alloimmune (isoimmune) response results in graft rejection, which is manifested as deterioration or complete loss of graft function. In contrast, autoimmunity is an immune response to the self's own antigens. Alloimmunization (isoimmunization) is the process of becoming alloimmune, that is, developing the relevant antibodies for the first time.

Antigen-presenting cell

An antigen-presenting cell (APC) or accessory cell is a cell that displays antigen complexed with major histocompatibility complexes (MHCs) on their surfaces; this process is known as antigen presentation. T cells may recognize these complexes using their T cell receptors (TCRs). APCs process antigens and present them to T-cells.

Clonal selection

Clonal selection theory is a scientific theory in immunology that explains the functions of cells (lymphocytes) of the immune system in response to specific antigens invading the body. The concept was introduced by the Australian doctor Frank Macfarlane Burnet in 1957, in an attempt to explain the formation of a diversity of antibodies during initiation of the immune response. The theory has become the widely accepted model for how the immune system responds to infection and how certain types of B and T lymphocytes are selected for destruction of specific antigens.

Innate immune system

The innate immune system is one of the two main immunity strategies found in vertebrates. The innate immune system is an older evolutionary defense strategy, relatively speaking, and it is the dominant immune system response found in plants, fungi, insects, and primitive multicellular organisms.

A breakthrough infection is a case of illness in which a vaccinated individual becomes sick from the same illness that the vaccine is meant to prevent. Simply, they occur when vaccines fail to provide immunity against the pathogen they are designed to target. Breakthrough infections have been identified in individuals immunized against a variety of different diseases including Mumps, Varicella, and Influenza. The character of breakthrough infections is dependent on the virus itself. Often, the infection in the vaccinated individual results in milder symptoms and is of a shorter duration than if the infection was contracted naturally.

Polyclonal B cell response

Polyclonal B cell response is a natural mode of immune response exhibited by the adaptive immune system of mammals. It ensures that a single antigen is recognized and attacked through its overlapping parts, called epitopes, by multiple clones of B cell.

In immunology, an adjuvant is a substance that potentiates and/or modulates the immune responses to an antigen to improve them. The word "adjuvant" comes from the Latin word adiuvare, meaning to help or aid. "An immunologic adjuvant is defined as any substance that acts to accelerate, prolong, or enhance antigen-specific immune responses when used in combination with specific vaccine antigens."

A non-specific immune cell is an immune cell that responds to many antigens, not just one antigen. Non-specific immune cells function in the first line of defense against infection or injury. The innate immune system is always present at the site of infection and ready to fight the bacteria; it can also be referred to as the "natural" immune system. The cells of the innate immune system do not have specific responses and respond to each foreign invader using the same mechanism. Methicillin-resistant Staphylococcus aureus (MRSA).

An experiment in immunology is a method of investigating immunological responses to antigens, or detecting and characterizing antibodies and lymphocytes. Findings from these experiments can be used to manipulate the immune system and develop drugs to combat immunological diseases.

Natural killer T (NKT) cells are a heterogeneous group of T cells that share properties of both T cells and natural killer cells. Many of these cells recognize the non-polymorphic CD1d molecule, an antigen-presenting molecule that binds self and foreign lipids and glycolipids. They constitute only approximately 0.1% of all peripheral blood T cells. Natural killer T cells should not be confused with natural killer cells.

Danger model

The Danger model is a theory of how the immune system works. It is based on the idea that the immune system does not distinguish between self and non-self, but rather between things that might cause damage and things that will not.

Immunological memory is the ability of the immune system to quickly and specifically recognize an antigen that the body has previously encountered and initiate a corresponding immune response. Generally these are secondary, tertiary and other subsequent immune responses to the same antigen. Immunological memory is responsible for the adaptive component of the immune system, special T and B cells — the so-called memory T and B cells. Immunological memory is the basis of vaccination.


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