Thus, innate immunity can have a memory, but it is not the same as learned immunological memory. Invertebrates have recently been shown to have "memory" of innate immune cells. The key distinctions between innate and adaptive memory are summarized in Table 1.
According to conventional opinion, the innate immune system has no memory of prior infections. In contrast, the adaptive immune system generates antibodies and cells that detect highly specific components of infections. It is believed that the innate immune system responds to all pathogens simultaneously, while the adaptive immune system takes time to respond only to certain types of pathogens.
It has now been shown that the innate immune system does have memory. Type I interferons (IFNs) are cytokines that play a major role in antiviral defense. They are produced by most cell types in response to viral infection or stress signals. Viruses have evolved many ways to block the action of type I IFNs, so they cannot be used as a defense against repeated infections with the same virus. However, it appears that the innate immune system has learned from past experience: it makes more type I IFNs after it has been activated once by a particular virus. This means that it has some form of immunological memory.
The original report on this topic was published in 2004. Since then, several other groups have also demonstrated that the innate immune system has memory. It is likely that this property helps the body to quickly produce high levels of type I IFNs upon re-exposure to viruses that cause little or no disease.
Immunological memory is a critical evolutionary characteristic that enhances host survival after reinfection. Memory is a feature of the immune system that is recognized by both the innate and adaptive arms. Immunological memory can be described as the ability of the immune system to remember previous exposures to pathogens, which allows for faster reaction upon re-exposure.
While immunological memory is essential for protecting humans and animals against repeated infections, it also contributes to autoimmune diseases and cancer. Understanding how the body creates long-term memories that last a life time is an important goal in science and medicine.
Immunological memory consists of two types: cellular and humoral. Cellular immune memory involves the formation of protective antibodies and cells that can kill invading pathogens immediately after exposure. Humoral immune memory refers to the creation of antibodies that protect against future attacks from the same pathogen. B cells are responsible for creating both forms of immunological memory.
Innate immune memory has been observed in many organisms from bacteria to mammals. It has been shown that genes involved in innate immunity are also required for the formation of cellular immune memory. For example, mice lacking the transcription factor NF-kappaB fail to form long-lasting protective antibodies following vaccination with bacterial antigens.
The adaptive immune response is more sophisticated than the innate immune response. When an antigen is detected, the adaptive immune system generates an army of immune cells that are particularly tailored to target that antigen. Adaptive immunity also has a "memory" that improves subsequent responses to a given antigen. In contrast, the innate immune system responds to many different types of pathogens with the same cells over and over again. It is not until after the initial attack against a virus or bacteria that our bodies start making antibodies.
In addition to these differences, the adaptive immune response cannot function without a previous exposure to the antigen that is trying to be recognized. Innate immunity does not rely on previous exposure to fight off infection. This is one reason why people who have never been exposed to HIV will always make antibodies against it even if they have never been infected with it before. But it is impossible to make antibodies against something if you have never been exposed to it.
In conclusion, the adaptive immune response is more sophisticated than the innate immune response. It relies on memory cells that can quickly be activated when needed again and again, which the innate immune system cannot do.
Immunological memory is the immune system's ability to respond with greater intensity when confronted with the same disease again, and it is the basis for vaccination (Ahmed and Gray, 1996). Memory cells are present in all major organ systems of the body. When exposed to the same antigen again, they rapidly produce more antibodies or T cells to fight off the disease.
When you receive a vaccine, your body creates memory cells that protect against disease. These cells are found in many organs such as the bone marrow, lymph nodes, skin, liver, and lungs. The presence of these memory cells helps the body better defend itself against future attacks from the disease.
There are two types of memory cells: short-lived effector cells and long-lived plasma cells. Short-lived effector cells fight off an infection immediately after being generated from memory stem cells. They last about one week before they are replaced by new cells. Long-lived plasma cells produce antibodies for months or years after receiving an initial stimulus from antigens. They live in the bone marrow until they are destroyed by cancer or old age.
The process of creating memory cells after being vaccinated shows that vaccines can induce immune responses even when you have already been exposed to the disease.
In conclusion, vaccination induces specific immune responses after an initial exposure to an antigen.