Final answer:
The first exposure to a pathogen triggers the primary adaptive response of the immune system, causing primary disease symptoms while it 'learns' the pathogen. Subsequent exposures lead to a faster and stronger secondary adaptive immune response, usually without symptoms, thanks to immunological memory. B and T cells play key roles in this process.
Step-by-step explanation:
The first time your body is exposed to a pathogen, the primary adaptive response of the adaptive immune system is initiated. This involves a process where the immune system has to learn how to recognize a pathogen and distinguish it from the body's own cells. Symptoms experienced during this phase, known as the primary disease, are relatively severe due to the time it takes for the adaptive immune response to become effective.
Upon re-exposure to the same pathogen, a secondary adaptive immune response is generated, which is stronger and faster than the primary response. This quick and vigorous response, based on immunological memory, often prevents the pathogen from causing significant tissue damage or symptoms. As a result, an individual may not even be aware of the infection.
The adaptive immune system has the amazing ability to learn from past infections and remember the pathogens it has encountered. This is done through the activity of B and T cells, which have receptors that can recognize specific antigens. Due to this sophisticated system, individuals have a decreased chance of suffering from the same illnesses repeatedly later in life.