Immune System - High School Biology

Adaptive immunity occurs when antibodies are produced as a result of exposure to a pathogen or immunization. These antibodies are specific for the particular microorganism and memory cells are produced. Cell-mediated immunity is a direct form of defense based on the action of lymphocytes to attack foreign cells and destroy them. Congenital immunity is immunity one is born with. This may result from antibodies received from the mother's blood. Innate immunity is not pathogen-specific and includes the secretion of proteins and the activities of natural killer cells. Passive immunity involves the introduction of preformed antibodies into an unprotected individual. This may occur through infusion of immune globulin or antibodies that pass from the mother to the fetus through the placenta.

VDJ recombination occurs during early B- and T-cell maturation, resulting in diverse antibodies and T-cells. This DNA recombination occurs between the V, D, and J segments of the antibody or T-cell before transcription occurs. As a result, a unique sequence is generated, transcribed, and then translated to a functional protein. This recombination is responsible for creating the unique series of antibodies that the body is capable of producing in order to detect the various antigens represented by foreign pathogens.

B cells and T cells are both part of the adaptive immunity. B cells secrete antibodies that bind to foreign antigens. Upon binding to a specific antigen, B cells can be activated by T cells, which facilitate the synthesis of specific antibodies for the antigen. This enhances the antibody-antigen binding and allows for a better immune response. T cells have receptors on their surface that detect antigens. Once they detect the antigen, T cells can activate B cells and other immune system cells (such as macrophages and neutrophils) to eliminate the foreign antigen. B cells do not play a role in the activation of T cells.

The question states that the immune complex has antibodies bound to antigens. Recall that B cells eliminate pathogens by secreting antibodies. These antibodies bind to antigens and release factors called cytokines. Cytokines recruit phagocytic cells like macrophages and neutrophils that kill the infected cell. They also activate a part of the innate immune system called the complement, which aids in the elimination of the pathogen. This type of immune response is called a humoral immune response. Elimination of the pathogen using T cells is called a cell-mediated immune response.

Note that both the humoral and the cell-mediated immune responses are very specific responses that are part of the adaptive immunity. Innate immunity involves non-specific immune responses via macrophages, granulocytes (neutrophils, eosinophils, and basophils), complement system, and NK cells.

Plasma cells are circulating cells that form part of adaptive immunity that secrete antibodies to specific antigens. These cells arise from naïve B cells. Broadly specific naïve B cells have the ability to bind to several antigens. Once bound, these naïve B cells differentiate into plasma cells that secrete antibodies that are very specific to the antigen. T cells facilitate this differentiation, but only B cells give rise to plasma cells.

A naïve T cell has the ability to differentiate into three kinds of cells. First, it can differentiate into a helper T cell. These cells facilitate the activation of other immune cells such as B cells, macrophages, and granulocytes. Second, a naïve T cell can differentiate into a cytotoxic T cell. These cells bind to infected cells and induce their death. Third, a naïve T cell can differentiate into a regulatory T cell. These T cells bind to the same antigens as the first two cells; however, instead of initiating an immune response, they regulate it by suppressing the activity of T cells.

HIV is a virus that likes to reside inside helper T cells. A person infected with HIV will have a decreased helper T cell count, which makes the person more susceptible to other opportunistic infections (infections that only occur in immune-compromised individuals). A patient with very low helper T cell count develops AIDS and often passes away due to these opportunistic infections.

There are three kinds of T cells: helper T cells, cytotoxic T cells, and regulatory T cells. All T cells have glycoproteins on their surfaces that act as receptors. CD4 and CD8 are two glycoproteins that can be found on T cells. Helper T cells and regulatory T cells have CD4 glycoproteins, whereas cytotoxic T cells have CD8. These glycoproteins serve as markers to distinguish between T cell types.

The question is asking about CD8, or cytotoxic, T cells. Recall that cytotoxic T cells bind to infected cells and induce their death. Typically, cytotoxic T cells bind to infected cells that have the pathogen inside them (meaning intracellular pathogens). Intracellular pathogens include viruses and intracellular bacteria; therefore, T cells that attack these cells will be CD8 cells. In addition, cytotoxic T cells also attack cancer cells; therefore, these T cells will also be CD8 cells.

Extracellular bacterial cells do not infect host cells; therefore, these bacteria are eliminated via the helper T cells. These T cells bind to the bacteria and activate other immune cells such as B cells, macrophages, and granulocytes that eliminate the bacteria.

Adaptive immunity involves immune cells created due to previously experiencing an infection by a particular pathogen. T-cell lymphocytes mature in the thymus, and recognize a specific antigen. T-cells and B-cells work to produce antibodies against a specific antigen, making them highly specific. This specification is only found in the adaptive immune system

In contrast, the innate immune system can respond to any pathogen, regardless of previous exposure, Neutrophils, monocytes, and macrophages are all part of the innate immune response and help with phagocytosis and inflammation.

Each B-lymphocyte cell is responsible for creating one specific antibody. If the B-lymphocyte's antibody matches to the right antigen, the lymphocyte will differentiate into a plasma cell. Plasma cells release free antibodies into the bloodstream. The transition process from B-cell to plasma cell is mediated by helper T-cells.

Memory B-cells are long-lived descendents of B-cells that "remember" their encounter with an antigen and can rapidly respond to reexposure to the same antigen. Helper T-cells stimulate the immune responses by B-cells and cytotoxic T-cells. B-cells produce antibodies. Macrophages destroy invading microbes via phagocytosis and alert other immune cells to the invasion. Effector molecules include histamine and the cell-destroying proteins of cytotoxic T-cells.

In response to infection, white blood cells multiply so that they can make antibodies against whatever it is your body is fighting off.

B-lymphocytes are the immune system's "memory"—once the body is attacked by a certain virus or bacteria, the body produces B-lymphocytes that can specifically recognize that disease. When the B-lymphocyte comes in contact with the disease (recognized by antibodies) it signals killer T-cells and helper T-cells to attack, and creates more antibodies to signal additional T-cells.

Natural killer cells destroy any cells of the human body that have become infected by an attacker.

Macrophages are a general clean-up cell that sweep up debris, old cells, and sometimes attackers via phagocytosis.

Killer and helper T-cells are both activated by B-lymphocytes

B cells make antibodies that are specific to antigens. Antibodies bind to antigens to tag them for destruction. Cytotoxic T cells recognize and bind antigens and destroy them immediately. Helper T cells recognize antigens presented by antigen-presenting cells such as dendridic cells, and bring them to the attention of B cells, stimulating the B cells to begin making lots of antibodies.

Innate immunity is defined as the general protection mechanisms from pathogens. Innate immunity will be present even when the body has not seen a specific pathogen. Antibodies are highly specific for one particular antigen, and only develop in the body after previous exposure to a pathogen. As a result, it is not considered innate. Instead, antibodies are considered a hallmark of adaptive immunity.

Physical barriers (like the skin), chemical barriers (like stomach acid), and non-specific immune cells (like phagocytes) help to protect against all pathogens, regardless of the type of pathogen or previous exposure.

Innate immunity is non-specific immunity linked to general defenses in the body. These immune defenses include inflammation and phagocytosis, which are not determined by the specific responses of B- or T-lymphocytes. Physical barriers, such as tight junctions in the skin and the acidity of the stomach and vaginal canal, also act as innate immune mechanisms.

Acquired and active immunity only result from a prior exposure to an antigen. Antibodies are produced by B-cells. Cell-mediated immunity involves the regulatory and cytotoxic activites of T-cells during the specific immune response. Humoral immunity is the term used to describe the protective activities of antibodies against infection by common microorganisms.

The innate immune system is a general defense against infections. Antibodies are very specific to the type of infection they can fight. Thus antibodies are considered specific defense.

Lymphocytes are part of the adaptive (specific) immune system, which monitors and dispatches in response to specific threats. The adaptive immune response utilizes antibody secretions from B-lymphocytes to target specific pathogens for elimination.

In contrast, the innate immune system is largely designed to prevent entry and propagation of non-specific pathogens. It is composed of barriers (such as skin and mucus linings) as well as non-specific immune cells (such as macrophages and natural killer cells).

The innate immune system is the part of your immune system that responds to threats almost immediately. It contains all the aspects which react to all threats and is generally seen as less complex than the adaptive immune system. The adaptive immune system includes aspects that respond to specific threats and develop memory to fight threats later on.