Immune System Overview and Innate Cells

The adaptive immune response is highly specific to a particular foreign agent. It can recognize and respond to previously unseen foreign molecules.

The adaptive immune response is able to remember past encounters with specific foreign molecules, mounting a faster and stronger response upon subsequent exposures.

The adaptive immune response relies on lymphocytes, a type of white blood cell, which have unique antigen receptors that recognize specific foreign molecules.

Clonal selection describes the process where lymphocytes with the right antigen receptors are selected to proliferate and fight against a specific pathogen.

Clonal expansion refers to the rapid division of selected lymphocytes, generating a large army of immune cells all specific to the same foreign molecule.

The stage where lymphocytes are activated. This occurs in the mucosa or lymph nodes near the infection site.

The effector phase, where lymphocytes and phagocytes migrate to the site of infection to fight the pathogen.

This type of adaptive immunity relies on B-cells and antibodies.

A type of immune defense that involves engulfing and destroying pathogens, primarily bacteria. This process is crucial for fighting bacterial infections.

A protein released by cells infected with a virus to warn nearby healthy cells. These cells can then activate antiviral mechanisms, hindering the virus's spread.

A type of immune response that occurs when the body's immune system overreacts to harmless substances, leading to damage to the body's tissues.

A condition where the body's immune system attacks its own tissues, mistaking them for foreign invaders.

The ability of the immune system to recognize and eliminate pathogens, preventing infection and protecting the body from disease.

The first line of defense against pathogens, involving physical barriers like skin and chemical barriers like stomach acid.

An immune response characterized by immediate, non-specific actions. It lacks memory for specific pathogens.

The immune response that adapts to specific pathogens, developing memory for future encounters.

Chemical messengers that recruit immune cells to the site of infection or inflammation.

A cascade of proteins that plays a vital role in the innate immune response, enhancing inflammation, destroying pathogens, and eliminating immune complexes.

A localized response to injury or infection, characterized by increased blood flow, vascular permeability, and cell recruitment.

A type of white blood cell with the innate ability to kill tumor and viral cells.

Cells residing in connective tissues and mucous membranes that release histamine and heparin during activation.

White blood cells that engulf and destroy pathogens through phagocytosis.

Large phagocytic cells residing in the tissues, derived from blood monocytes. They also play a role in antigen presentation.

Antigen presenting cells that process foreign material and present it to lymphocytes.

Short-lived phagocytes containing hydrolytic enzymes and toxic molecules. They are crucial for defense against extracellular bacteria.

White blood cells related to neutrophils, releasing histamine and playing a role in defense against parasites and allergic reactions.

The process by which NK cells kill cells by creating holes in their membranes, allowing proteases to enter and induce cell apoptosis.

A process of programmed cell death that dismantles the cell without releasing its contents, preventing the spread of viruses.

Antigen-presenting cells (APCs) are cells that display antigens to T lymphocytes, initiating an immune response. They include macrophages, dendritic cells, and B cells.

MHC class II molecules are found on the surface of APCs and present antigens to CD4+ T cells, primarily helper T cells (Th cells).

MHC class I molecules are present on all nucleated cells in the body and present antigens to CD8+ T cells, primarily cytotoxic T lymphocytes (CTLs).

The human leukocyte antigen (HLA) system is a genetic region responsible for the expression of MHC molecules. HLA genes vary among individuals, contributing to the diversity of immune responses.

IgG is the most abundant antibody in the blood, lymph, and cerebrospinal fluid. It provides long-term immunity, crosses the placenta, and acts as an opsonizing antibody, which enhances phagocytosis.

IgA is found in mucosal secretions (saliva, tears, breast milk) and protects against infections at mucosal surfaces, like the respiratory tract and gastrointestinal tract. It prevents pathogens from attaching to and penetrating the epithelial surface.

IgM is the first antibody produced during an immune response, activating the complement system and signaling recent infection or exposure to an antigen.

IgE binds to receptors on mast cells and basophils, causing the release of histamine and leading to type 1 hypersensitivity reactions, like allergic reactions.

IgD's exact function is not fully understood, but it is involved in B cell development and activation.

A TH1 response is associated with type 1 hypersensitivity reactions, like hayfever. Macrophages present antigens to TH1 cells, leading to the activation of macrophages and cytotoxic T cells.

A TH2 response is associated with type 4 hypersensitivity reactions, like contact dermatitis. Antibodies present antigens to TH2 cells, leading to IgE production and allergic reactions.

The Fab region of an antibody binds to the specific antigen, making it the antigen-binding site. It recognizes and attaches to the specific target molecule.

The Fc region of an antibody binds to various receptors on cells or to the first component of the complement system. It initiates downstream signaling and effector functions.

Antibodies consist of four chains: two light chains and two heavy chains. The structure of the heavy chains determines the antibody class (IgG, IgA, IgM, IgE, IgD).

The complement system is a series of proteins in the blood that act in a cascade, leading to the lysis of cell membranes, recruitment of immune cells, and opsonization of pathogens. It is activated by antibodies or directly by pathogens.

T cells are immune cells that mature in the thymus and are responsible for cell-mediated immunity. They are critical for targeting and destroying infected cells. T cells come in two main types: Cytotoxic T cells (CD8+) - kill infected cells and Helper T cells (CD4+) - control the type of immune response.

Cytotoxic T cells (Tc) are a type of T cell that directly destroy infected cells. They recognize antigens presented on MHC Class I molecules, which are found on all nucleated cells in the body. When a Tc cell detects an infected cell, it releases cytotoxic granules containing proteins that induce apoptosis (programmed cell death).

Helper T cells (Th) are a type of T cell that help other immune cells perform their functions. They recognize antigens presented on MHC Class II molecules, which are found on antigen-presenting cells (APCs) like macrophages and B cells. Th cells secrete cytokines that activate other immune cells, such as macrophages, B cells, and other T cells.

TH1 cells are a subtype of Helper T cell that primarily promotes cell-mediated immunity. They secrete cytokines like interferon-gamma (IFN-γ) that activate macrophages and other T cells, leading to the killing of infected cells.

TH2 cells are a subtype of Helper T cell that primarily promotes antibody-mediated immunity. They secrete cytokines like interleukin-4 (IL-4) and interleukin-5 (IL-5) that activate B cells to produce antibodies.

MHC (Major Histocompatibility Complex) molecules are cell surface proteins involved in the recognition of antigens by T cells. They present processed fragments of antigens to T cells, initiating the immune response. There are two main classes: MHC Class I and MHC Class II.

MHC Class I molecules are found on all nucleated cells in the body. They present peptides from inside the cell, such as viral proteins, to cytotoxic T cells (CD8+).

MHC Class II molecules are found on antigen-presenting cells (APCs) like macrophages and B cells. They present peptides derived from phagocytized pathogens to helper T cells (CD4+).

Antigen-presenting cells (APCs) are specialized cells that capture and present antigens to T cells, initiating the immune response. Key examples include macrophages, dendritic cells, and B cells.

T cells are crucial for adaptive immunity. They are responsible for recognizing specific antigens and initiating targeted immune responses against them, such as eliminating infected cells or activating B cells to produce antibodies.

The thymus is a primary lymphoid organ located in the chest. It is the site where T cells mature and develop their ability to recognize and respond to specific antigens.

Lymphoid follicles are areas within secondary lymphoid organs, like lymph nodes and the spleen, that are rich in B cells. B cells proliferate and mature their antibody responses within these follicles.

The paracortex is a region in the lymph node where T cells reside. Antigen-presenting cells (APCs) present antigens to T cells in the paracortex, triggering T cell activation and differentiation.

Mucosa-associated lymphoid tissues (MALT) are specialized collections of lymphoid tissues found in the mucosal linings of the body. They are critical for defending the body against pathogens entering through mucous membranes.

The immune system relies on a delicate balance between TH1 and TH2 responses to ensure proper functioning. TH1 promotes cell-mediated immunity, while TH2 promotes antibody-mediated immunity. This balance is crucial for an effective immune response against various pathogens.

Involves the release of histamine and other chemicals from mast cells and basophils, causing rapid symptoms like swelling, itching, and difficulty breathing.

Mediated by antibodies that target antigens on cell surfaces or in the extracellular matrix, leading to cell destruction.

Involves immune complexes formed by antigen and antibody binding, which can then deposit in tissues and cause inflammation.

Delayed response primarily mediated by T-cells, resulting in inflammation and tissue damage, occurring hours or days after exposure to the antigen.

A disorder where the immune system is compromised, making the individual more susceptible to infections.

A severe, life-threatening allergic reaction that can cause widespread swelling, difficulty breathing, and circulatory collapse.

A type of autoimmune disorder affecting the thyroid gland, causing an overproduction of thyroid hormones.

A systemic autoimmune disorder characterized by inflammation and damage in multiple organs, including the joints, skin, kidneys, and nervous system.

A type of T-cell responsible for initiating tissue damage in autoimmune disorders.

Antibodies that target the body's own tissues, contributing to the pathogenesis of autoimmune disorders.

A mechanism that prevents the immune system from attacking healthy tissues.

The ability of the immune system to fight infections and disease.

A type of immunodeficiency present at birth, usually due to genetic factors.

A type of immunodeficiency acquired later in life, often due to factors like infection, malnutrition, or medications.