Natural immunity, also known as innate immunity, refers to the immune defenses that a person is born with. It provides the first line of defense against pathogens (like bacteria, viruses, and parasites), and it's a generalized form of protection that does not target specific threats. Unlike adaptive immunity, which develops after exposure to specific pathogens or vaccines, innate immunity is non-specific and is present from birth.

There are several components of natural immunity:

1. Physical barriers: These include the skin and the mucous membranes lining the respiratory, gastrointestinal, and genitourinary tracts. These barriers block most pathogens from entering the body. In addition, substances like mucus, sweat, and tears contain antimicrobial compounds that help kill pathogens.
2. Cellular defenses: The immune system has several types of cells that help fight off pathogens. These include phagocytes, like neutrophils and macrophages, which ingest and destroy pathogens. Natural killer cells, another type of immune cell, can recognize and kill certain virus-infected cells and cancer cells.
3. Inflammatory response: This is a response triggered by damage to body tissues. Inflammation helps to isolate and repair the damaged area, and it also helps to attract immune cells to the site of the infection or injury.
4. Fever: A higher body temperature can enhance the immune response and inhibit the growth of some pathogens.
5. Complement system: This is a system of proteins that enhances (complements) the ability of antibodies and phagocytic cells to clear pathogens from an organism.

Natural immunity forms a crucial part of the body's defense mechanism. However, in some cases, it might not be enough to fully protect against disease. This is particularly true for certain bacteria and viruses that have strategies to evade the immune system. In these cases, the body relies on adaptive immunity, which provides a more targeted and efficient response to specific pathogens.

The interaction between natural immunity and adaptive immunity is a major factor in how the body responds to infections. For example, someone who has been infected with a disease and recovered typically has an adaptive immune response, made up of antibodies and T-cells that can recognize and respond to the same pathogen in the future. This is the basis of natural immunity to re-infection. However, the duration and effectiveness of this immunity can vary greatly, depending on the pathogen and the individual's immune response. It's important to note that while natural immunity can be protective, it can also sometimes come with severe or life-threatening disease symptoms, which is why vaccines are important - they stimulate the immune system to provide protection without causing the disease itself.