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From wikipedia & other reliable sources ( Poets, Writers, Thinkers, Researchers, Free Lancers, Philosophers, Theologists, Scientists, Orators, Sociologists and Photographers +Artists-Musicians & etc.) we can learn as follows :
World Health Organization (WHO)
In biology, immunity is the capability of multicellular organisms to resist harmful microorganisms. Immunity involves both specific and nonspecific components. The nonspecific components act as barriers or eliminators of a wide range of pathogens irrespective of their antigenic make-up. Other components of the immune system adapt themselves to each new disease encountered and can generate pathogen-specific immunity.
Immunity is a complex biological system that can recognize and tolerate whatever belongs to the self, and to recognize and reject what is foreign (non-self).[1]
Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals.[1][2] The gastrointestinal metagenome is the aggregate of all the genomes of the gut microbiota.[3][4] The gut is the main location of the human microbiome.[5] The gut microbiota has broad impacts, including effects on colonization, resistance to pathogens, maintaining the intestinal epithelium, metabolizing dietary and pharmaceutical compounds, controlling immune function, and even behavior through the gut–brain axis.
The microbial composition of the gut microbiota varies across regions of the digestive tract. The colon contains the highest microbial density recorded in any habitat on Earth, representing between 300 and 1000 different species.[6] Bacteria are the largest and to date, best studied component and 99% of gut bacteria come from about 30 or 40 species.[7] Up to 60% of the dry mass of feces is bacteria.[8] Over 99% of the bacteria in the gut are anaerobes, but in the cecum, aerobic bacteria reach high densities.[5] It is estimated that the human gut microbiota have around a hundred times as many genes as there are in the human genome.
The establishment of a gut flora is crucial to the health of an adult, as well as the functioning of the gastrointestinal tract.[49] In humans, a gut flora similar to an adult's is formed within one to two years of birth as microbiota are acquired through parent-to-child transmission and transfer from food, water, and other environmental sources.[50][10]
The traditional view of the gastrointestinal tract of a normal fetus is that it is sterile, although this view has been challenged in the past few years.[51] Multiple lines of evidence have begun to emerge that suggest there may be bacteria in the intrauterine environment. In humans, research has shown that microbial colonization may occur in the fetus[52] with one study showing Lactobacillus and Bifidobacterium species were present in placental biopsies.[53] Several rodent studies have demonstrated the presence of bacteria in the amniotic fluid and placenta, as well as in the meconium of babies born by sterile cesarean section.[54][55] In another study, researchers administered a culture of bacteria orally to a pregnant dam, and detected the bacteria in the offspring, likely resulting from transmission between the digestive tract and amniotic fluid via the blood stream.[56] However, researchers caution that the source of these intrauterine bacteria, whether they are alive, and their role, is not yet understood.[57][53]
During birth and rapidly thereafter, bacteria from the mother and the surrounding environment colonize the infant's gut.[10] The exact sources of bacteria is not fully understood, but may include the birth canal, other people (parents, siblings, hospital workers), breastmilk, food, and the general environment with which the infant interacts.[58] Research has shown that the microbiome of babies born vaginally differ significantly from those of babies delivered by caesarean section and that vaginally born babies got most of their gut bacteria from their mother, while the microbiota of caesarean babies had more bacteria associated with hospital environments.[59]
During the first year of life, the composition of the gut flora is generally simple and changes a great deal with time and is not the same across individuals.[10] The initial bacterial population are generally facultative anaerobic organisms; investigators believe that these initial colonizers decrease the oxygen concentration in the gut, which in turn allows obligately anaerobic bacteria like Bacteroidota, Actinomycetota, and Bacillota to become established and thrive.[10] Breast-fed babies become dominated by bifidobacteria, possibly due to the contents of bifidobacterial growth factors in breast milk, and by the fact that breast milk carries prebiotic components, allowing for healthy bacterial growth.[53][60] In contrast, the microbiota of formula-fed infants is more diverse, with high numbers of Enterobacteriaceae, enterococci, bifidobacteria, Bacteroides, and clostridia.[61]
Caesarean section, antibiotics, and formula feeding may alter the gut microbiome composition.[53] Children treated with antibiotics have less stable, and less diverse floral communities.[62] Caesarean sections have been shown to be disruptive to mother-offspring transmission of bacteria, which impacts the overall health of the offspring by raising risks of disease such as celiacs, asthma, and type 1 diabetes.[53] This further evidences the importance of a healthy gut microbiome. Various methods of microbiome restoration are being explored, typically involving exposing the infant to maternal vaginal contents, and oral probiotics.[53]
Functions
Innate Immunity First off, the immune system is a system in the body of animals that enables animals to avoid or limit many infections caused by pathogens. Pathogens are disease causing agents, causing a wide range of illnesses. As for Diseases it's when structure of an organism is negatively affected other than external injury. Both diseases and pathogens affect the immune system causing illness to specific animals. Animals has a form of innate immunity. In invertebrates, they have Barrier defenses Phagocytosis and Antimicrobial peptides. As for Vertebrates they have Barrier defenses, phagocytosis, antimicrobial peptides, natural killer cells, antimicrobial proteins, and inflammatory response. Barrier Defenses Barrier Defenses include skin, mucous, lysozyme, and acidic pH in the stomach and on the skin. The barrier defense like the skin prevents pathogens from entering, not only that the skin is a physical barrier that secretes oil with a high pH. Other Physical barriers include eyelids, lashes, mucous, and a very acidic stomach. All these physical immune system help defend against pathogens that occur in everyday life. Phagocytosis Phagocytosis is a type of white blood cell that helps breaks down pathogenic bacteria in your body. The phagocytotic cell types are Neutrophils and Macrophages. Neutrophils circulate in the bloods and Macrophages is in the connective tissues which are big eaters. Natural Killer Cells Natural killer cells circulate in the blood. Natural Killer Cells detect against virus and cancer cells, Natural killer cells release chemical that leads to cell death, though this is only in vertebrates only. Maternal natural killer cells transfer anti-microbial peptide granulysin through a nanotube to kill an infection in the cell of a placenta. Natural killer cells can attack extracellular and intracellular pathogens, killing off pathogens that can create illnesses within the body. Antimicrobial Peptides Antimicrobial peptides kill pathogens, they disorder membranes. Some Antimicrobial peptides kill both bacteria and fungi. Not only that they can interfere with DNA and protein synthesis. In addition, antimicrobial peptides demonstrate to have a variety of functions for example clearance of infection and induce pro-inflammatory cytokine production. Inflammatory response Inflammatory response is a response where upon injury the specific place becomes inflamed and warm to the touch. The reason why the site of injury becomes red and warm is because of the blood vessel dilation, causing warming and redish color. The messengers are Cytokines and Histamines. Cytokines are produced by macrophages recruit neutrophils. Histamines are produced by mast cells triggering blood vessels dilation of capillaries.
Scheme of a Fc receptor The immune system has innate and adaptive components. Innate immunity is present in all metazoans,[2] while adaptive immunity only occurs in vertebrates.The innate component of the immunity system involves the recognition of certain foreign (non-self) molecules to generate one of two types of innate immune responses: inflammatory responses and phagocytosis.[3] The adaptive component, on the other hand, involves more advanced lymphatic cells that can distinguish between specific "non-self" substances in the presence of "self". The reaction to foreign substances is etymologically described as inflammation while the non-reaction to self substances is described as immunity. The two components of the immune system create a dynamic biological environment where "health" can be seen as a physical state where the self is immunologically spared, and what is foreign is inflammatorily and immunologically eliminated. "Disease" can arise when what is foreign cannot be eliminated or what is self is not spared.[4]
Innate immunity, also known as native immunity, is a semi-specific and widely distributed form of immunity. It is defined as the first line of defense against pathogens, representing a critical systemic response to prevent infection and maintain homeostasis, contributing to the activation of an adaptive immune response.[5] It does not adapt to specific external stimulus or a prior infection, but relies on genetically encoded recognition of particular patterns.[6]
Adaptive or acquired immunity is the active component of the host immune response, mediated by antigen-specific lymphocytes. Unlike the innate immunity, the acquired immunity is highly specific to a particular pathogen, including the development of immunological memory.[7] Like the innate system, the acquired system includes both humoral immunity components and cell-mediated immunity components.[citation needed]
Adaptive immunity can be acquired either 'naturally' (by infection) or 'artificially' (through deliberate actions such as vaccination). Adaptive immunity can also be classified as 'active' or 'passive'. Active immunity is acquired through the exposure to a pathogen, which triggers the production of antibodies by the immune system.[8] Passive immunity is acquired through the transfer of antibodies or activated T-cells derived from an immune host either artificially or through the placenta; it is short-lived, requiring booster doses for continued immunity.
The diagram below summarizes these divisions of immunity. Adaptive immunity recognizes more diverse patterns. Unlike innate immunity it is associated with memory of the pathogen. [6]
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