Innate vs Adaptive Immunity

iC3Bb is a key enzyme in the alternative complement pathway. It cleaves C3, a crucial protein in the immune system, into C3b and C3a.

C3b is an important protein fragment generated from C3 cleavage by iC3Bb. It binds to the pathogen surface and plays a crucial role in targeting them for destruction.

C3a is a small protein fragment released when C3 is cleaved. It acts as an anaphylatoxin, attracting immune cells to the site of infection.

CR1 is a receptor found on macrophages, specialized cells that engulf and destroy pathogens. It binds to C3b, the 'flag' on pathogens, facilitating phagocytosis.

Factor I is a protein that regulates the complement system. It cleaves C3b into iC3b, inhibiting the formation of C3 convertase and preventing excessive complement activation.

Factor H is a protein that protects healthy cells from complement attack. It prevents C3b from binding to the host cell surface and recruits Factor I to cleave C3b into iC3b.

The alternative complement pathway is a critical part of the innate immune system. It helps to control infections by targeting pathogens directly through the formation of a membrane attack complex (MAC).

C3bBb is a powerful C3 convertase formed in the alternative complement pathway. It further cleaves C3, amplifying the response and coating the pathogen surface with C3b.

A deficiency in C3 leads to an increased susceptibility to infections caused by encapsulated bacteria. This is because C3 is crucial for initiating the complement cascade, which helps the immune system recognize and eliminate these bacteria.

A deficiency in C5-C9 leads to an increased susceptibility to infections caused by Neisseria bacteria, such as gonorrhea and meningitis.

A deficiency in Factor D or Properdin (factor P) leads to an increased susceptibility to infections caused by both encapsulated bacteria and Neisseria species.

The membrane attack complex (MAC) is a pore-forming structure that destroys pathogens by disrupting their cell membrane. It is formed by the terminal components of the complement system, C5b-C9.

C3a and C5a are small fragments produced during the complement cascade. They act as anaphylatoxins, causing degranulation of mast cells and basophils, leading to increased vascular permeability, vasodilation, and recruitment of inflammatory cells.

Anaphylactic shock is a severe allergic reaction characterized by a sudden drop in blood pressure, difficulty breathing, and swelling of the face and throat. It can be triggered by the release of large amounts of histamine from mast cells and basophils, often caused by anaphylatoxins like C3a and C5a.

The alternative pathway of the complement system is a way to activate the system without the need for antibodies. It is particularly important for defense against encapsulated bacteria and certain viruses.

C3b is a breakdown product of C3. It binds to the surface of pathogens, marking them for destruction by phagocytic cells. C3b is a critical component of the complement system because it helps link the innate and adaptive immune responses.

Random joining of V, D, and J gene segments during B cell development, leading to a diverse repertoire of B cell receptors.

The ability of any light chain to associate with any heavy chain, further expanding the diversity of B cell receptors.

This process adds or removes nucleotides during recombination, increasing the variability of the B cell receptor's antigen-binding site (CDR3).

P nucleotides are added during the recombination process by DNA polymerase, resulting from the filling of gaps created by the opening of hairpin loops.

Exonucleases can remove nucleotides during recombination, including P nucleotides, adding to the diversity of the CDR3 region.

TdT adds non-templated nucleotides to the DNA during recombination in the heavy chain, increasing the diversity of the CDR3 region.

This antigen-dependent process occurs after antigen exposure and improves the affinity of B cell receptors for their target antigen.

The 12/23 rule ensures that V, D, and J gene segments recombine correctly by pairing 12-base pair RSSs with 23-base pair RSSs.

Lactoferrin is a protein found in secondary granules that binds iron, making it unavailable for bacteria to use. This prevents bacterial growth by depriving them of essential nutrients.

Azurophilic granules are found in neutrophils and contain powerful enzymes that help break down pathogens. They play a crucial role in the destruction of engulfed microbes during phagocytosis.

Natural Killer (NK) cells are part of the innate immune system and kill virus-infected cells and tumor cells. They recognize and eliminate cells that lack MHC-1 molecules, a marker that identifies healthy cells.

IL-12 is a cytokine produced by macrophages and dendritic cells. It activates NK cells and promotes the production of IFN-gamma, which further enhances macrophage activity. This positive feedback loop amplifies the immune response.

Neutrophils are the first responders to infection, migrating from the blood to the site of infection. They are the most abundant type of white blood cell and play a key role in phagocytizing and destroying pathogens.

Neutrophilia is a condition where the neutrophil count in the blood is higher than normal. It often indicates an acute bacterial infection or inflammation.

Neutropenia is a condition where the neutrophil count in the blood is lower than normal. It can occur during chronic or overwhelming infections, making the body more susceptible to infections.

Mast cells are innate immune cells that release inflammatory mediators like histamine and cytokines, contributing to the inflammatory response. They are triggered by PRRs recognizing PAMPs or by Ag binding to IgE.

A stage in T cell development where immature thymocytes express both CD4 and CD8 coreceptors. They are called double positive (DP) cells.

A process where thymocytes interact with antigen-presenting cells (APCs) in the thymus, particularly mTECs (medullary thymic epithelial cells). This interaction helps select for T cells that can recognize self-MHC molecules, ensuring proper immune function.

A mechanism that eliminates thymocytes that recognize self-antigens too strongly, preventing autoimmunity. This process occurs in the thymus and involves interaction with mTECs expressing self-antigens.

A type of T cell that exits the thymus before going through positive or negative selection. They are distinct from conventional alpha-beta T cells and have unique functions.

A type of medullary thymic epithelial cell (mTEC) that plays a crucial role in T cell development. They express a wide range of self-antigens and participate in both positive and negative selection.

The first signal required for T cell activation. It's initiated when a T cell receptor (TCR) on a naive T cell binds to a specific antigen-peptide complex presented on an MHC molecule of an antigen-presenting cell (APC).

The second signal required for T cell activation. It's provided by the interaction between the B7 molecule (CD80/86) on an APC and the CD28 molecule on a T cell. This co-stimulation enhances T cell activation and ensures appropriate responses.

The third signal required for T cell activation. It determines the T cell's fate by instructing it to differentiate into a specific effector T cell. This signal often involves cytokines released by APCs or other immune cells.

CXCL8 (IL-8) is a chemokine that attracts neutrophils to the site of inflammation. CXCL8 binds to its receptor on neutrophils, inducing cell signaling that increases the affinity of integrins, which helps the neutrophils bind to and migrate through the endothelium.

Integrins are adhesion molecules found on immune cells. They bind to ICAMs (intercellular adhesion molecules) on endothelial cells, stopping immune cells from rolling and allowing them to adhere to the vessel wall.

Selectins are adhesion molecules found on endothelial cells that bind to ligands on immune cells. IL-1 and TNF-α increase the expression of selectins on the endothelium, enhancing the initial rolling of immune cells.

Neutrophils are the first responders to infection. They undergo a multi-step process to reach the site of infection, starting with rolling adhesion, followed by tight adhesion, and finally diapedesis.

Neutrophils contain three types of granules: secretory, gelatinase, and specific granules. Secretory and ficolin-1 granules are the last to form but the first to be released. They are necessary for neutrophils to attach to the endothelium and extravasate into the tissue. Gelatinase granules contain gelatinase and arginase, which help neutrophils extravasate and degrade extracellular matrix.

The phagosome is an intracellular vesicle formed when a neutrophil engulfs a pathogen. The early phagosome is characterized by oxygen-dependent reactions, which produce reactive oxygen species (ROS) and reactive nitrogen species (RNS) that kill bacteria by damaging DNA and metabolic pathways. These reactions are initiated by NADPH oxidase, superoxide dismutase (SOD), and myeloperoxidase (MPO).

The phagolysosome is formed when a phagosome fuses with a lysosome. This fusion brings lysozyme and acid hydrolases into the phagosome, promoting the breakdown of the pathogen. This process is oxygen-independent and occurs in the later stages of pathogen killing.

Band neutrophils are immature neutrophils that lack secretory and ficolin-1 granules. They are unable to attach to the endothelium and extravasate into the tissue effectively.