defense response to Gram-positive bacterium

Definition

Target type: biologicalprocess

Reactions triggered in response to the presence of a Gram-positive bacterium that act to protect the cell or organism. [GOC:ai]

The defense response to Gram-positive bacteria is a complex and multi-layered process involving both innate and adaptive immune responses.

**Innate Immune Response:**

* **Recognition:** Pattern recognition receptors (PRRs) on immune cells, like macrophages and neutrophils, recognize pathogen-associated molecular patterns (PAMPs) specific to Gram-positive bacteria. These PAMPs include peptidoglycan (PGN), lipoteichoic acid (LTA), and flagellin.
* **Phagocytosis:** Macrophages and neutrophils engulf and internalize Gram-positive bacteria through phagocytosis. This process is facilitated by opsonization, where antibodies or complement proteins bind to the bacterial surface, enhancing recognition and uptake.
* **Intracellular killing:** Once internalized, the bacteria are exposed to a variety of antimicrobial mechanisms within the phagosome. These include:
* **Reactive oxygen species (ROS):** Superoxide anions, hydrogen peroxide, and other ROS are generated by NADPH oxidase, causing oxidative damage to bacterial components.
* **Reactive nitrogen species (RNS):** Nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) also contributes to bacterial killing.
* **Lysosomal enzymes:** Lysosomes fuse with the phagosome, releasing proteases, lipases, and other enzymes that degrade bacterial components.
* **Antimicrobial peptides:** Defensins, cathelicidins, and other antimicrobial peptides are released by immune cells and directly target bacterial membranes, disrupting their integrity.

**Adaptive Immune Response:**

* **Antigen presentation:** Macrophages and dendritic cells process bacterial antigens and present them to T cells, triggering the adaptive immune response.
* **T cell activation:** T cells, particularly CD4+ helper T cells, recognize bacterial antigens presented by MHC class II molecules on antigen-presenting cells. This activation leads to the production of cytokines, such as IL-2, IL-4, and IFN-γ, which further modulate immune responses.
* **B cell activation:** Activated T cells interact with B cells, leading to the production of antibodies specific to bacterial antigens.
* **Antibody-mediated immunity:** Antibodies bind to bacterial surface antigens, promoting opsonization, complement activation, and neutralization of bacterial toxins.

**Other Key Factors:**

* **Complement system:** The complement system is activated by PGN and LTA, leading to the formation of the membrane attack complex (MAC), which can lyse bacteria.
* **Inflammation:** The release of inflammatory mediators, such as cytokines and chemokines, recruits immune cells to the site of infection and promotes tissue repair.

This coordinated defense response aims to eliminate the Gram-positive bacteria, prevent their spread, and minimize tissue damage.'
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Proteins (24)

Compounds (941)