The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens,from viruses to parasitic worms,as well as cancer cells and objects such as wood splinters,distinguishing them from the organism's own healthy tissue. Many species have two major subsystems of the immune system. The innate immune system provides a preconfigured response to broad groups of situations and stimuli. The adaptive immune system provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use molecules and cells to perform their functions.
The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding anatomical sites in which they reside,including the gastrointestinal tract,skin,mammary glands,seminal fluid,uterus,ovarian follicles,lung,saliva,oral mucosa,conjunctiva,and the biliary tract. Types of human microbiota include bacteria,archaea,fungi,protists,and viruses. Though micro-animals can also live on the human body,they are typically excluded from this definition. In the context of genomics,the term human microbiome is sometimes used to refer to the collective genomes of resident microorganisms;however,the term human metagenome has the same meaning.
Neutrophils are a type of white blood cell. More specifically,they form the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system,with their functions varying in different animals.
The adaptive immune system,also known as the acquired immune system,or specific immune system is a subsystem of the immune system that is composed of specialized,systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system is one of the two main immunity strategies found in vertebrates.
An opportunistic infection is an infection caused by pathogens that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources,such as a weakened immune system,an altered microbiome,or breached integumentary barriers. Many of these pathogens do not necessarily cause disease in a healthy host that has a non-compromised immune system,and can,in some cases,act as commensals until the balance of the immune system is disrupted. Opportunistic infections can also be attributed to pathogens which cause mild illness in healthy individuals but lead to more serious illness when given the opportunity to take advantage of an immunocompromised host.
Pathogen-associated molecular patterns (PAMPs) are small molecular motifs conserved within a class of microbes,but not present in the host. They are recognized by toll-like receptors (TLRs) and other pattern recognition receptors (PRRs) in both plants and animals. This allows the innate immune system to recognize pathogens and thus,protect the host from infection.
In cell biology,a phagosome is a vesicle formed around a particle engulfed by a phagocyte via phagocytosis. Professional phagocytes include macrophages,neutrophils,and dendritic cells (DCs).
Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host. They are also called intracellular pathogens.
The innate immune system or nonspecific immune system is one of the two main immunity strategies in vertebrates. The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants,fungi,prokaryotes,and invertebrates.
Virulence factors are cellular structures,molecules and regulatory systems that enable microbial pathogens to achieve the following:
Dysbiosis is characterized by a disruption to the microbiome resulting in an imbalance in the microbiota,changes in their functional composition and metabolic activities,or a shift in their local distribution. For example,a part of the human microbiota such as the skin flora,gut flora,or vaginal flora,can become deranged,with normally dominating species underrepresented and normally outcompeted or contained species increasing to fill the void. Similar to the human gut microbiome,diverse microbes colonize the plant rhizosphere,and dysbiosis in the rhizosphere,can negatively impact plant health. Dysbiosis is most commonly reported as a condition in the gastrointestinal tract or plant rhizosphere.
Bacteria are ubiquitous,mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length,bacteria were among the first life forms to appear on Earth,and are present in most of its habitats. Bacteria inhabit soil,water,acidic hot springs,radioactive waste,and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the fixation of nitrogen from the atmosphere. The nutrient cycle includes the decomposition of dead bodies;bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps,extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds,such as hydrogen sulphide and methane,to energy. Bacteria also live in mutualistic,commensal and parasitic relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be grown in the laboratory. The study of bacteria is known as bacteriology,a branch of microbiology.
Porphyromonas gingivalis belongs to the phylum Bacteroidota and is a nonmotile,Gram-negative,rod-shaped,anaerobic,pathogenic bacterium. It forms black colonies on blood agar.
Pathogenic bacteria are bacteria that can cause disease. This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and are often beneficial but others can cause infectious diseases. The number of these pathogenic species in humans is estimated to be fewer than a hundred. By contrast,several thousand species are part of the gut flora present in the digestive tract.
Microbiota are the range of microorganisms that may be commensal,mutualistic,or pathogenic found in and on all multicellular organisms,including plants. Microbiota include bacteria,archaea,protists,fungi,and viruses,and have been found to be crucial for immunologic,hormonal,and metabolic homeostasis of their host.
Cellular microbiology is a discipline that bridges microbiology and cell biology.
In molecular biology,the guanylate-binding proteins family is a family of GTPases that is induced by interferon (IFN)-gamma. GTPases induced by IFN-gamma are key to the protective immunity against microbial and viral pathogens. These GTPases are classified into three groups:the small 47-KD immunity-related GTPases (IRGs),the Mx proteins,and the large 65- to 67-kd GTPases. Guanylate-binding proteins (GBP) fall into the last class.
Colonization resistance is the mechanism whereby the intestinal microbiota protects itself against incursion by new and often harmful microorganisms.
In biology,a pathogen,in the oldest and broadest sense,is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent,or simply a germ.
Siderocalin(Scn),lipocalin-2,NGAL,24p3 is a mammalian lipocalin-type protein that can prevent iron acquisition by pathogenic bacteria by binding siderophores,which are iron-binding chelators made by microorganisms. Iron serves as a key nutrient in host-pathogen interactions,and pathogens can acquire iron from the host organism via synthesis and release siderophores such as enterobactin. Siderocalin is a part of the mammalian defence mechanism and acts as an antibacterial agent. Crystallographic studies of Scn demonstrated that it includes a calyx,a ligand-binding domain that is lined with polar cationic groups. Central to the siderophore/siderocalin recognition mechanism are hybrid electrostatic/cation-pi interactions. To evade the host defences,pathogens evolved to produce structurally varied siderophores that would not be recognized by siderocalin,allowing the bacteria to acquire iron.
