What is a white blood cell with solid nucleus and clear cytoplasm?

A white blood cell with a solid nucleus and clear cytoplasm is called a lymphocyte. Lymphocytes are a type of white blood cell that play a role in the body's immune system. They are produced in the bone marrow and thymus gland. There are two main types of lymphocytes: T lymphocytes (T cells) and B lymphocytes (B cells). T cells help to kill infected cells and cancer cells, while B cells produce antibodies to help fight off infections.