Lymphocytes and plasma cells are specialized immune cells that help protect the body against infection. Large numbers of these cells are not usually seen a tissue sample from the normal, healthy colon is examined under the microscope. Basal lymphoplasmacytosis means that a large groups of lymphocytes and plasma cells were seen in tissue that lines the inside of the colon.
This change is caused by abnormal activation of the immune system. What triggers the immune system to become activated is not currently known.