Pathologists use the term basal lymphoplasmacytosis to describe large groups of specialized lymphocytes and plasma cells in the tissue that lines the inside of the colon. Because large groups of lymphocytes and plasma cells are not normally seen in the colon, basal lymphoplasmacytosis is used to support the diagnosis of chronic colitis. Chronic colitis is a condition where prolonged or chronic inflammation damages the colon and prevents it from working normally.
Basal lymphoplasmacytosis is caused by abnormal activation of the immune system. What triggers the immune system to become activated is not currently known. Other signs of prolonged inflammation in the colon are crypt distortion and Paneth cell metaplasia.