Lymphocytes are a type of white blood cell (leukocyte) that play a central role in the body’s immune system. The help recognize and respond to infections, eliminate abnormal cells, and provide long-term immune memory after exposure to pathogens or vaccination

Lymphocytes originate from stem cells in the bone marrow. After maturation, lymphocytes circulate through blood, lymphatic vessels, lymph nodes, spleen and mucosal tissues. Most lymphocytes are found in lymphoid tissues rather than circulating in the bloodstream.

Lymphocytes in pleural fluid can provide important clues about the cause of a pleural effusion (fluid around the lungs). The significance depends on how many lymphocytes are present, the overall cell count, and other pleural fluid test results.

A pleural effusion is considered lymphocyte-predominant when lymphocytes make up more than 50% of the white blood cells in the fluid. Common causes include Tuberculosis, Malignancies, Lympoma, chronic heart failure and viral infections.