Final answer:
Lymphopenia is the condition characterized by a decreased number of circulating lymphocytes in the blood, often associated with chronic illness or immunosuppressive conditions such as HIV or steroid therapies.
Step-by-step explanation:
Lymphopenia refers to a decreased number of circulating lymphocytes in the blood. Lymphocytes, which include T cells, B cells, and NK cells, are a type of white blood cell essential for the immune response. They are formed from lymphoid stem cells and account for about 20-30 percent of all leukocytes. A normal lymphocyte count is crucial for a robust immune system. However, when an individual has lymphopenia, their lymphocyte count is abnormally low, which can be characteristic of chronic illness or immunosuppression. Such immunosuppression may be due to factors such as HIV infection or certain drug therapies, often involving steroids.
Conditions like leukopenia, where there is a below-normal production of leukocytes, can lead to an increased risk of infection as the body's ability to ward off disease is compromised. Conversely, leukocytosis, an excessive proliferation of leukocytes, may result in high leukocyte counts, but these cells are often nonfunctional, which also leaves the individual susceptible to disease.
It's important to note that while lymphopenia focuses on the low count of lymphocytes specifically, other related conditions such as leukemia and lymphoma deal with abnormalities in leukocytes production, affecting the overall immune system's capacity to function properly.