Inate defence against infection Flashcards
The host response to microbial infection
The host response to microbial infection involves a complex interplay between the invading microbe and the host’s immune system. The host’s immune system is a complex network of cells, tissues, and organs that work together to defend the body against infection.
When a microbe enters the body, the immune system recognizes it as foreign and mounts a response to eliminate it. This response can take several forms, including the activation of innate immune cells such as neutrophils and macrophages, which engulf and destroy the invading microbe.
In addition to innate immunity, the host also relies on adaptive immunity, which involves the activation of T cells and B cells that can specifically recognize and target the invading microbe.
During the immune response, various cytokines and chemokines are produced, which act as chemical messengers to attract immune cells to the site of infection and activate them. This can result in inflammation, which is a normal part of the immune response but can also contribute to tissue damage.
If the immune response is successful, the microbe is eliminated, and the infection is resolved. However, in some cases, the immune response can be ineffective or even harmful, leading to chronic infections or autoimmune diseases. Therefore, understanding the host response to microbial infection is critical for developing effective strategies to prevent and treat infectious diseases.
explain humoural immune response and adaptive immune response
The humoral immune response and adaptive immune response are two different components of the immune system that work together to protect the body from invading pathogens.
The humoral immune response involves the production of antibodies by B cells in response to an invading pathogen. Antibodies are proteins that specifically recognize and bind to antigens on the surface of the pathogen, marking it for destruction by other components of the immune system, such as phagocytes. This process is called opsonization, and it helps to eliminate the pathogen from the body.
The adaptive immune response, on the other hand, involves the activation of T cells and B cells that are specific to the invading pathogen. T cells recognize and destroy infected cells, while B cells produce antibodies that target the pathogen. The adaptive immune response takes longer to develop than the humoral immune response, but it is more specific and can provide long-lasting immunity against future infections.
The adaptive immune response requires the recognition of specific antigens by immune cells, which is facilitated by the major histocompatibility complex (MHC) molecules. MHC molecules present antigens to T cells, which recognize and respond to specific antigens. This process is called antigen presentation.
Both the humoral and adaptive immune responses are essential for protecting the body from infectious diseases. Together, they provide a multi-layered defense that can recognize and eliminate a wide range of pathogens.
▪ Mechanical barriers to infection
Skin: The skin is the largest organ of the body and serves as a physical barrier to pathogens. It prevents microorganisms from entering the body by providing a tough, waterproof layer that covers the entire body.
Mucous membranes: Mucous membranes are found in various parts of the body, including the nose, mouth, eyes, and genitals. They produce mucus, a sticky substance that traps pathogens and prevents them from entering the body.
Cilia: Cilia are tiny hair-like structures that line the respiratory tract and other parts of the body. They move back and forth, pushing mucus and trapped pathogens out of the body.
Tears: Tears are produced by the lacrimal glands and help to flush out bacteria and other pathogens from the eyes.
Saliva: Saliva contains enzymes and antibodies that can kill bacteria and viruses.
Urine flow: Urine flow helps to flush out bacteria from the urinary tract, preventing infection.
Vomiting and diarrhea: Vomiting and diarrhea are the body’s natural defenses against ingested pathogens. They help to expel harmful substances from the body before they can cause further harm.
explain the The complement system in host defence
Activation: The complement system can be activated through three different pathways - classical, lectin, and alternative pathways. All three pathways lead to the activation of a series of complement proteins, which are numbered from C1 to C9.
Opsonization: The complement proteins bind to the surface of the invading microorganism, a process called opsonization. This makes it easier for phagocytic cells, such as neutrophils and macrophages, to engulf and destroy the microorganism.
Inflammation: The complement proteins also trigger an inflammatory response by activating mast cells and recruiting neutrophils and macrophages to the site of infection. This leads to an increased blood flow and swelling in the affected area, which helps to contain the infection.
Membrane attack: The final step in the complement cascade is the formation of the membrane attack complex (MAC). The MAC is a complex of complement proteins that creates a pore in the membrane of the microorganism, leading to its destruction.
explain The acute inflammatory response
Vasodilation: The first step in the acute inflammatory response is vasodilation, which occurs in response to the release of various chemical mediators such as histamine, prostaglandins, and leukotrienes. Vasodilation causes the blood vessels in the affected area to widen, which increases blood flow to the area and allows more immune cells to reach the site of injury.
Increased vascular permeability: As blood vessels widen, the permeability of the blood vessel walls increases, allowing fluid and proteins to leak into the surrounding tissues. This leads to swelling or edema at the site of injury.
Chemotaxis: The chemical signals released by the damaged tissue and immune cells attract other immune cells to the site of injury through a process called chemotaxis. This brings neutrophils, monocytes, and other immune cells to the site of injury, where they can initiate the process of tissue repair.
Activation of immune cells: Once immune cells reach the site of injury, they become activated and start to release cytokines and chemokines, which attract additional immune cells to the area. This creates a positive feedback loop that amplifies the inflammatory response.
Phagocytosis: Neutrophils and monocytes are phagocytic cells that can engulf and digest bacteria, dead cells, and other debris at the site of injury. This process is called phagocytosis, and it is an important part of the acute inflammatory response.
Resolution: As the tissue repair process begins, the acute inflammatory response starts to resolve. This is characterized by a decrease in vascular permeability and a decrease in the number of immune cells at the site of injury. The resolution of the acute inflammatory response is essential for tissue healing and repair to occur.
Natural killer cells
Natural killer (NK) cells are a type of immune cell that plays a critical role in the body’s defense against viruses, bacteria, and cancer cells. They are called “natural” killers because they do not require prior exposure to a specific pathogen to recognize and attack it. Instead, they are able to detect and destroy infected or abnormal cells through their innate immune system.
NK cells are able to recognize and kill target cells by identifying specific surface markers or ligands on these cells. These markers may be absent or altered on infected or cancerous cells, allowing the NK cells to differentiate between healthy and abnormal cells. Once an NK cell recognizes an abnormal or infected cell, it releases cytotoxic granules containing perforin and granzymes that cause cell death through apoptosis.
Chemical defence
Antimicrobial peptides: These are small proteins that are able to kill a broad range of pathogens, including bacteria, viruses, and fungi. They are produced by various cells in the body, including skin cells, and mucous membranes.
Enzymes: Certain enzymes found in various fluids in the body, such as lysozyme in tears and saliva, can break down the cell walls of bacteria and other pathogens.
Acidity: The stomach has a very low pH due to the presence of hydrochloric acid, which can kill many pathogens that are ingested.
Mucus: The mucous membranes in the body produce a thick, sticky substance called mucus that can trap pathogens and prevent them from entering the body.
Sweat: Sweat contains a variety of chemicals, including salt, that can inhibit the growth of bacteria and fungi.
