How does plasma membrance play an important role in generating immune responses
Answers
it may contain receptors
Answer:
Have you ever wondered how a virus or other infectious agent invades a cell to start an infection? Many cells need to bring a variety of materials, like bacteria, dead host cells, and debris from other cells or the environment, across their plasma membrane and into their cytoplasm for many different reasons. Some cells can use various methods, such as ion pumps, voltage-gated channels, or osmosis, to pull smaller molecules and chemicals across the plasma membrane and into their cytoplasm. But larger objects, like viruses, bacteria, or other particles are too large to use small channels to transport through the plasma membrane. So, cells engulf the larger objects and pull them in, which is generally called endocytosis. There are many different types of endocytosis, one of which is called phagocytosis.
What is phagocytosis?
Phagocytosis is a process wherein a cell binds to the item it wants to engulf on the cell surface and draws the item inward while engulfing around it. The process of phagocytosis often happens when the cell is trying to destroy something, like a virus or an infected cell, and is often used by immune system cells.
Phagocytosis differs from other methods of endocytosis because it is very specific and depends on the cell being able to bind to the item it wants to engulf by way of cell surface receptors. Phagocytosis won’t happen unless the cell is in physical contact with the particle it wants to engulf.
The cell surface receptors used for phagocytosis depends on the type of cell that is doing the phagocytizing. These are the most common ones:
Opsonin receptors: Opsonin receptors are used to bind bacteria or other particles that have been coated with immunoglobulin G (or “IgG”) antibodies by the immune system. The immune system coats potential threats in antibodies so that other cells know it needs to be destroyed. The immune system can also use something called the “complement system”, which is a group of proteins used to tag the bacteria. The complement system is another way for the immune system to destroy pathogens and threats to the host.
Scavenger receptors: Scavenger receptors bind to molecules that are produced by bacteria. Most bacteria and other cellular species produce a matrix of proteins surrounding themselves (called an “extracellular matrix”). This matrix is a perfect way for the immune system to identify foreign species in the body, because human cells do not produce the same protein matrix.
Toll-like receptors: Toll-like receptors, named after a similar receptor in fruit flies encoded by the Toll gene, bind to specific molecules produced by bacteria. Toll-like receptors are a key part of the innate immune system because, once bound to a bacterial pathogen, they recognize the specific bacteria and activate the immune response. There are lots of different types of Toll-like receptors produced by the body, all which bind different molecules.
Antibodies: Some immune cells make antibodies that can bind to specific antigens. This is a process similar to how toll-like receptors recognize and identify what type of bacteria is infecting the host. Antigens are molecules that act like a pathogen “calling card”, because they help the immune system know what threat it has to fight.
How does phagocytosis happen?
Cells have to complete some steps in order to successfully phagocytize something. In order to illustrate this a little easier, let’s say we are following a macrophage (a type of immune cell) phagocytizing a virus. Keep in mind, a lot of different types of cells perform phagocytosis, though.
The virus and the cell need to come into contact with each other.
Sometimes the immune cell accidentally bumps into a virus in the blood stream. Other times, cells move by way of a process called “chemotaxis”. Chemotaxis means the movement of an organism or cell in response to a chemical stimulus. Many immune system cells move in response to cytokines, small proteins used specifically for cell signaling. Cytokines signal cells to move to certain area in the body where the particle (in our case, a virus) is found. This is common with infections that are specific to a certain area (like a skin wound infected with bacteria).
The virus binds to the cell surface receptors on the macrophage.
Remember that different cell types express different receptors. Some receptors are general, meaning that they can identify a self-produced molecule versus a potential threat (and that’s about it), and others are very specific, like toll-like receptors or antibodies. The macrophage will not initiate phagocytosis without successful binding of the cell surface receptors.
Explanation: