Conditions That Cause Lymphocytosis

Lymphocytosis is a term used to describe a condition in which an individual has a higher than normal amount of lymphocytes in their blood. Lymphocytes are white blood cells that fight off pathogens and reside in the lymphatic system. They do this by differentiating into memory cells to recognize pathogens the body has seen before and by differentiating into plasma cells that make antibodies to fight the pathogen off. While a high lymphocyte count is relatively normal following a recent infection, it is not normal for it to stay elevated. When the lymphocyte count exceeds three thousand lymphocytes in a microliter of blood, it is lymphocytosis. No symptoms present with lymphocytosis itself, but the symptoms of the underlying cause may be apparent. A complete blood count with differential can help a physician determine if an individual is affected lymphocytosis. A bone marrow biopsy may also be utilized to help identify the underlying cause of an individual's lymphocytosis.

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Whooping Cough


Whooping cough (pertussis) is a highly contagious infection of the respiratory tract. The hallmark symptoms of whooping cough include a severe hacking cough trailed by a 'whoop' sound upon inhalation. A bacteria called Bordetella pertussis causes whooping cough. This bacteria has a specialized and unique ability to impair the function of the affected individual's immune system through its actions on lymphocytes. While the exact mechanism of how whooping cough induces lymphocytosis is not clear, it is known to be associated with the production increase in mIL-4 or interleukin-4 triggered by the pertussis virus. The toxin produced by the pertussis bacteria causes phagocyte cells to make too much cyclic AMP by converting ATP or cellular energy. This malfunction results in a disruption in signaling mechanisms the immune system uses to respond to infection. Because of these signaling disturbances, the bacteria have a selective influence on the ability of lymphocytes to enter the lymph nodes. When lymphocytes cannot enter the lymphatic system, they accumulate in the affected individual's blood causing a lymphocyte count of over four thousand per microliter of blood.

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HealthPrep Staff