Final answer:
The term that indicates a decrease in the number of lymphocytes is lymphopenia, which is caused by conditions like chronic illness or immunosuppressive treatments.
Step-by-step explanation:
The term that indicates a decrease in the number of lymphocytes is lymphopenia. This condition is often associated with chronic illness or immunosuppression, which can be caused by conditions such as HIV infection or treatments that include steroids. Lymphocytes, which include various T cells, B cells, and NK cells, are a type of leukocyte essential for the immune response, and they are generated from lymphoid stem cells. In contrast, leukocytosis refers to an abnormally high number of white blood cells, and neutropenia is a decrease in neutrophils, another type of white blood cell. Pancytopenia is a condition where there is a decrease in all types of blood cells.