Follicular Lymphoma is a type of non-Hodgkin lymphoma. It develops when the body makes abnormal B-lymphocytes – the lymphoma cells. (B-lymphocytes are white blood cells that fight infection). The lymphoma cells build up in lymph nodes. The most common symptom is a painless swelling in the neck, armpit or groin. low-grade non-Hodgkin lymphoma. It is a slow-growing lymphoma that develops from B lymphocytes (B cells). It is called 'follicular' lymphoma because the abnormal lymphocytes often collect in lymph nodes in clumps that are known as 'follicles'.