lecture 15 and 16 Flashcards
Compare and contrast antibody-mediated (humoral) and cell-mediated (cellular) immunity.
Humoral immunity is primarily mediated by B cells, which produce antibodies. In contrast, cell-mediated immunity is facilitated by T cells, specifically T-helper cells and cytotoxic T cells. They are both branches of the adaptive immune system that works together to protect the body.
o Humoral - Humoral immunity is most effective against extracellular pathogens, such as bacteria and viruses in body fluids. Cell-mediated immunity targets intracellular pathogens, including viruses, some bacteria, and cancer cells
o Cell-mediated
T cells directly interact with infected cells or activate other immune cells
Cytotoxic T lymphocytes (CTLs) destroy cells displaying foreign antigens
It activates macrophages and natural killer (NK) cells to destroy intracellular pathogens
types of humoral immunity
B cells produce antibodies that circulate in body fluids
Antibodies bind to specific antigens, neutralizing pathogens or marking them for destruction.
It is a major defense mechanism against extracellular microbes
describe antibody structure
o Antibodies, also known as immunoglobulins, are large Y-shaped glycoproteins that play a crucial role in the immune system. The basic structure of an antibody consists of four polypeptide chains: two identical heavy chains and two identical light chains
o has a Y-shaped structure composed of four polypeptide chains: two identical heavy chains and two identical light chains, which are held together by disulfide bonds; the “arms” of the Y are formed by the variable regions of both heavy and light chains, allowing for specific antigen binding, while the stem of the Y is the constant region, responsible for interacting with immune cells to trigger immune responses; each antibody has two identical antigen-binding sites at the tips of the Y arms, enabling it to bind to specific antigens with high specificity
Describe mechanisms of antibody action.
o Antibodies function by specifically binding to antigens on foreign particles, like pathogens or toxins, and neutralizing them through mechanisms like neutralization, opsonization, and complement activation; essentially, they either directly block the pathogen’s activity, tag it for destruction by immune cells like macrophages, or trigger a cascade of complement proteins to lyse (burst) the target cell.
neutralization in antibody action
Neutralization - Antibodies bind to critical sites on a pathogen, such as a virus’s receptor-binding domain, preventing it from interacting with host cells and causing infection
opsonization in antibody action
Opsonization - By binding to an antigen, antibodies “tag” the pathogen, making it more recognizable to phagocytes (like macrophages and neutrophils) which then engulf and destroy it
complement activation in antibody action
Complement activation - Antibodies can trigger the complement cascade, a series of protein reactions that ultimately lead to the formation of a membrane attack complex on the pathogen’s cell membrane, causing it to lyse
.Interpret a graph of the primary and secondary immune response, in terms of the relative concentrations of different classes of antibodies produced over time.
o A graph illustrating the primary and secondary immune responses typically shows a significantly higher and faster peak in antibody concentration during the secondary response compared to the primary response, with the initial primary response often producing primarily IgM antibodies followed by a gradual shift to IgG, while the secondary response rapidly produces high levels of IgG due to the presence of memory B cells, resulting in a quicker and more robust immune reaction upon re-exposure to the same antigen
Distinguish between active and passive immunity.
o Active - Immunity developed when the body’s immune system actively produces antibodies against a specific pathogen. The body is exposed to a pathogen, such as an infection of vaccination which then triggers the immune system to create antibodies and memory cells
o Passive - Immunity obtained by receiving pre-made antibodies from another source. Antibodies are transferred from a donor, such as a mother to her baby through breast milk or placenta, or through an injection of antibodies (immunoglobulin therapy)
natural active immunity versus natural passive immunity
o Natural active immunity occurs when your body develops antibodies by fighting off an infection naturally, like recovering from the chickenpox, while artificial active immunity is when you receive a vaccine to stimulate your immune system to produce antibodies against a specific disease, like the measles vaccine.
o natural passive immunity happens when a baby receives antibodies from their mother through the placenta or breastmilk, and artificial passive immunity is when someone receives a concentrated dose of antibodies through an injection, like immunoglobulin therapy for a snake bite
define antigen
An antigen is any substance that can trigger an immune response by binding to specific receptors on immune cells, essentially signaling to the body that a foreign substance is present and needs to be targeted.
define self-antigen
a self-antigen is an antigen that belongs to the body itself, normally not triggering an immune response
define antigen receptor
an antigen receptor is a protein on the surface of immune cells that specifically binds to a particular antigen, allowing the immune system to recognize and respond to it
Describe where class I and class II major histocompatibility complex (MHC) proteins are found.
o Class I MHC proteins are found on the surface of nearly all nucleated cells in the body, while class II MHC proteins are primarily expressed on antigen-presenting cells (APCs) like macrophages, dendritic cells, and B cells; meaning class I is more widely distributed than class I
o Class 1 - Present on almost all cells in the body due to their role in presenting peptides derived from inside the cell to the immune system, which is crucial for detecting infected cells
o Class 2 - Found primarily on APCs, which are specialized immune cells responsible for capturing and presenting extracellular antigens to T cells
Explain the functions of class I and class II major histocompatibility complex (MHC) proteins in adaptive (specific) immunity.
o Class I MHC proteins present peptides derived from intracellular antigens on the surface of all nucleated cells, alerting the immune system to potential infections within the cell and triggering cytotoxic CD8+ T cell responses.
o Class II MHC proteins, expressed only on antigen-presenting cells like macrophages and dendritic cells, present peptides from extracellular pathogens to activate CD4+ helper T cells, which coordinate the immune response
what are antigen presenting cells
o Antigen-presenting cells (APCs) are immune cells that play a crucial role in initiating adaptive immune responses by capturing, processing, and presenting antigens on their surface using Major Histocompatibility Complex (MHC) molecules, which allows them to activate T cells and trigger an immune response against specific pathogens.
examples of APCs
o key examples of APCs include dendritic cells, macrophages, and B cells, with dendritic cells being considered the most potent APC due to their ability to activate naïve T cells
Helper T cell
o Helper T cells - These cells act as the “commanders” of the immune response, activating other immune cells like cytotoxic T cells and B cells by releasing cytokines (signaling molecules) when they encounter an antigen; they are crucial for coordinating the immune response against pathogens
cytotoxic T cell
o Cytotoxic T cells - Also called “killer T cells”, these directly destroy infected cells or cancerous cells by releasing cytotoxic substances that trigger programmed cell death (apoptosis)
regulatory (suppressor) T cell
o Regulatory (suppressor) T cells - These cells play a crucial role in suppressing the immune response, preventing excessive immune reactions and maintaining self-tolerance, thus preventing autoimmune diseases
B cell
o B cells - When activated by an antigen, B cells differentiate into plasma cells, which produce antibodies that specifically bind to the antigen, marking it for destruction by other immune cells
plasma cell
o Plasma cells - These are mature B cells that actively secrete large quantities of antibodies specific to a particular antigen
memory cell
o Memory cells - Both B and T cells can develop into memory cells, which remain in the body after an initial infection and rapidly respond to future encounters with the same pathogen, providing long-term immunity.
immunocompetence
o Immunocompetence refers to the ability of an immune system to mount a normal immune response against foreign antigens, meaning it can recognize and effectively react to pathogens
