The body’s natural immune system has two components: innate and adaptive immunity. Innate immunity is a broad immediate immune response. The adaptive immune response is a targeted response to a specific pathogen, taking about a week to fully develop.
The human body can immediately respond to a potentially dangerous infection. Our immune system does this by recognizing essential and unchanging components of viruses, bacteria, or other pathogens. These are called Pathogen Associated Molecular Patterns (PAMPs). These structures are found in or on the pathogen, but are not found in our body. There are many different PAMPs, which are specific to different classes of pathogens. This allows our body to target any pathogens that carry these structures. Our body do this by carrying Pattern Recognition Receptors (called PRRs). There are many different types of PRRs in the body; each one recognizes a different PAMP. PRRs sit on the outside of immune cells, waiting to engage PAMPs.
When a PRR recognizes a PAMP, it triggers a large number of proteins in the cell to go to work. The cell ramps up its defenses, at the same time sending signals to other cells to start doing the same. It’s very similar to the mobilization of an army, with different cell types starting to do whatever it is they are designed to do. Some of the protein fighters include interferons, which can help combat infections or cancer, and cytokines, which can help coordinate the defense.
The innate response doesn’t just result in an immune response against the foreign pathogen—it sends signals to our adaptive immune system to start a highly-targeted response. The adaptive immune response is a complex process that can result in direct killing of infected cells and it includes antibody responses against pathogens. Because it is specific to a particular pathogen, it takes time to generate the directed response. However, once our body has done this, it maintains a memory of the pathogen. It takes much less time to generate the adaptive response the next time we see the same pathogen. Unfortunately, there are many different types of viruses and bacteria that can cause illnesses and these can mutate rapidly to escape our immune defenses. This is one reason why the innate immune system broadly targets the parts of pathogens that cannot change—so we can be assured of mounting an immune response against just about anything dangerous with which we come in contact.