Adaptive Immune Defenses and Blood Types

An antigen is any substance that can mobilize adaptive defenses and provoke an immune response. They are often large, complex molecules that are not normally found in the body. Antigens are recognized as intruders, the 'non-self' by the immune system.

Antigen presenting cells are cells that do not respond to specific antigens, rather they play essential auxiliary roles in immunity, A key role they play is to help T cells recognize antigens. T cells cannot recognize antigens without the help of antigen presenting cells.

The clonal section of B cells is the process by which B cells are activated through binding to an antigen. The binding of the antigen to the B cell surface receptors cross-links them and triggers receptor-mediated endocytosis. The B cell then proliferates into a clone of cells, and differentiates to into effector cells or memory cells.

<p>Active humoral immunity is the result of the body's own immune response to an antigen. Passive humoral immunity involves the transfer of antibodies from another source to the body.</p> Signup and view all the answers

<p>Antibodies are Y-shaped proteins with two identical heavy chains and two identical light chains. The variable regions of the antibody (at the tips of the Y) bind to specific antigens. The constant regions (at the stem of the Y) determine the antibody class and dictate its function. Antibodies can bind to cells or chemical targets in order to inactivate them. They may also serve to target antigens for destruction by various components of the immune system.</p> Signup and view all the answers

<p>T cell activation is a two-step process that starts with antigen presentation by an antigen presenting cell. The T cell antigen receptor (TCR) must recognize both the MHC protein and the foreign antigen displayed on the MHC protein. Once double-recognition of the antigen has occurred, the TCR is activated, and T cell proliferation and differentiation begin.</p> Signup and view all the answers

<p>Helper T cells are a type of T cell that is critical for the humoral and cellular immune responses - primarily because they help to activate other cells in the immune system. They also directly regulate the immune response by releasing cytokines.</p> Signup and view all the answers

<p>Cytotoxic T cells recognize target cells, and directly kill infected or abnormal cells through a process called apoptosis. They are particularly important for eliminating virus-infected cells, cancerous cells, and other foreign cells. Regulatory T cells are another type of T cell that has a different role. These cells help to suppress the immune response and prevent autoimmune reactions. They help to regulate the immune response and prevent the immune system from attacking the body's own cells. They are essential for maintaining immune system tolerance.</p> Signup and view all the answers

<p>The two branches are humoral and cellular responses. Humoral immunity is mediated by antibodies. Cellular immunity directly involves T lymphocytes.</p> Signup and view all the answers

<p>Specificity: the ability to recognize multiple different antigens, but only one at a time. Memory: stronger/enhanced response upon repeat exposure. Clonal expansion of lymphocytes: rapid proliferation to tackle microbial expansion, using B and T lymphocytes. Specialization: optimized response to different antigens. Systemic: not restricted to the infection site. Speed: the adaptive immune response is slower than the innate immune response.</p> Signup and view all the answers

<p>Complete antigens have two important properties - immunogenicity (the ability to stimulate proliferation of specific lymphocytes) and reactivity (the ability to react with activated lymphocytes and antibodies). Incomplete antigens are very small molecules that are not immunogenic by themselves. They become immunogenic only when they attach to a larger carrier molecule, such as a protein.</p> Signup and view all the answers

<p>Antigenic determinants are the specific parts of an antigen that antibodies or lymphocyte receptors bind to. Most antigens have multiple antigenic determinants, which is why the immune system can generate a wide variety of antibodies against them.</p> Signup and view all the answers

<p>MHC proteins are glycoproteins found on the surface of all cells. They are coded by genes of the major histocompatibility complex. They act as identifiers, allowing the body's immune system to recognize and respond to foreign antigens. Millions of gene combinations make MHCs unique to each individual, making it difficult to find a suitable donor for organ transplants.</p> Signup and view all the answers

<p>T cells, B cells, and antigen presenting cells. T cells are responsible for cellular immunity. B cells are responsible for humoral immunity. Antigen presenting cells are essential for T cell activation.</p> Signup and view all the answers

<p>B cells are involved in humoral immunity and are responsible for the production of antibodies. They mature in the bone marrow. T cells are involved in cellular immunity and mature in the thymus. These cells are both directly involved in destroying foreign invaders. They also both form memory cells that can be used for future responses.</p> Signup and view all the answers

<p>B cells mature in the bone marrow and T cells mature in the thymus.</p> Signup and view all the answers

<p>Antigen receptor diversity is a result of the shuffling of gene segments that code for antigen receptors. Each T cell has its own unique antigen receptor, which is important for recognizing a broad range of antigens.</p> Signup and view all the answers

<p>The major types of antigen presenting cells (APCs) are dendritic cells, macrophages, and B cells. Dendritic cells are commonly located at body boundaries, such as the skin, and travel to the lymph nodes to activate T cells. Macrophages live in the body tissues and engulf foreign material. B cells are important for the humoral response.</p> Signup and view all the answers

<p>Double recognition is the process by which T cells recognize both the MHC protein and the foreign antigen that is being presented by an APC. This two-part recognition safeguards against unwanted or premature T cell activation. It ensures that T cells are only activated when it is safe to do so, and in response to a genuine threat to the body.</p> Signup and view all the answers

<p>A vaccine typically consists of a weakened or dead form of the pathogen. This is sometimes referred to as an antigen. The antigen is introduced into the body, which triggers the immune response, but the body does not get sick from the weakened form. The immune system recognizes the antigen and mounts an attack, resulting in the production of antibodies that are specific to that pathogen. This leaves the person ready for an immune response if the active form of the pathogen enters the body.</p> Signup and view all the answers

<p>CD4 cells can become Helper T cells (TH) – which activate B cells and other T cells. CD8 cells can become Cytotoxic T cells (TC) – which directly kill infected cells.</p> Signup and view all the answers

<p>Antigens are presented to developing T cells by antigen presenting cells (APCs). APCs engulf the antigen and process it into smaller fragments. They then present those fragments on MHC proteins (MHC Class I or Class II) located on their cell surface, and the T cell recognizes the combination. This process triggers T cell activation.</p> Signup and view all the answers

<p>Helper T cells (TH) are central to the adaptive immune response. They activate both the humoral and cellular immune responses by helping to activate both B cells and other T cells. They play a role in T and B cell proliferation and secrete cytokines that recruit even more immune cells. TH cells are essential for triggering a strong and effective immune response in the body. Without them, the immune system is not able to mount an adequate and robust response to foreign invaders.</p> Signup and view all the answers

<p>Helper T cells (TH) release interleukins that function as co-stimulatory signals to complete B cell activation. B cells can be activated without TH cells by T cell-independent antigens but the activation is weak and short-lived.</p> Signup and view all the answers

<p>Helper T cells (TH) amplify innate defenses by releasing cytokines, which stimulate macrophages, increasing their killing power. They also mobilize lymphocytes and macrophages to the site of infection, and recruit other white blood cells.</p> Signup and view all the answers

<p>Regulatory T cells (Treg) are a type of T cell that helps to dampen the immune response through direct cell contact or by secreting inhibitory cytokines. They play a major role in preventing autoimmune reactions. Current clinical research into this area is investigating their use for inducing tolerance to transplanted tissue.</p> Signup and view all the answers

<p>Cytotoxic T cells (Tc) directly attack and kill other cells. They are particularly involved in the elimination of virus-infected cells, cancerous cells, and other foreign cells. They release perforins and granzymes to achieve this.</p> Signup and view all the answers

<p>Cytotoxic T cells (Tc) deliver a lethal hit using two mechanisms: the release of perforins and granzymes, and the interaction with specific membrane receptors. Perforins create pores in the cell membrane allowing granzymes to enter and stimulate apoptosis. Tc cells can also trigger apoptosis through membrane receptor interactions.</p> Signup and view all the answers

<p>Natural killer (NK) cells recognize other signs of abnormality that cytotoxic T cells do not look for, such as cells that lack MHC proteins entirely. NK cells also target cells that have been coated with antibodies and cells that are expressing different surface markers. Instead of double recognition, NK cells utilize a variety of other markers, like the lack of MHC, or cells that are stressed. NK cells use the same key mechanisms as Tc cells but they are part of the innate immune response.</p> Signup and view all the answers

<p>Cytokines are chemical messengers of the immune system, which help to mediate cell development, differentiation, and responses in the immune system. They amplify and regulate both innate and adaptive immune responses. For example, gamma interferon increases the killing power of macrophages. Other well-known examples are interferons and interleukins.</p> Signup and view all the answers

<p>HIV targets CD4 cells, which are a type of helper T cell. Once HIV enters the CD4 cell, it uses reverse transcriptase to produce DNA from its viral RNA. This DNA copy is then integrated into the host cell's DNA, converting the cell into a viral factory. This leads to the production of new HIV particles, which infect other CD4 cells. HIV also results in a progressive decline in the number of CD4 cells, leaving the patient vulnerable to opportunistic infections.</p> Signup and view all the answers

<p>Helper T cells (TH) are involved in both humoral and cellular immunity as they assist in the activation of both B cells and other T cells. They release cytokines and are considered to act both directly and indirectly. Cytotoxic T cells (Tc) are responsible for eliminating infected or abnormal cells; they directly kill cells.</p> Signup and view all the answers

<p>Regulatory T cells (Treg) are important for preventing autoimmune disorders. They help to suppress the immune response and prevent the immune system from attacking the body's own tissues. Without Treg cells, the immune system would be prone to attacking its own tissues.</p> Signup and view all the answers

<p>Cytotoxic T cells (Tc) deliver a lethal hit using two mechanisms: the release of perforins and granzymes, and the interaction with specific membrane receptors. Perforins create pores in the target cell membrane allowing granzymes to enter and stimulate target cell apoptosis. Tc cells can also trigger apoptosis through membrane receptor interactions.</p> Signup and view all the answers

<p>ABO incompatibility is a problem the first time a transfusion is given because the recipient's plasma already contains antibodies against the donor's blood group. An Rh-negative person does not normally have anti-Rh antibodies, but these antibodies begin to develop after exposure to Rh-positive blood. The first Rh-exposure does not cause a problem because the anti-Rh antibodies develop slowly. A second Rh-exposure is a problem because the recipient's immune system has already developed antibodies against Rh-positive blood, and these antibodies can attack donated Rh-positive red blood cells, leading to a transfusion reaction.</p> Signup and view all the answers

<p>A person with type A blood can receive type A or type O blood. To receive blood, the recipient must have the same blood type as the donor or be type O. A person with type A blood cannot receive type B or type AB blood, as that would lead to a transfusion reaction.</p> Signup and view all the answers

<p>A person with type O negative blood is considered to be a universal donor because they do not have any antigens on their red blood cells that could trigger an immune response in the recipient. A person with type AB positive blood is considered to be a universal acceptor because they have all three ABO antigens on their red blood cells (A, B, and Rh) so they will not react to any blood type.</p> Signup and view all the answers