One of the most common outcomes of pulp inflammation is periapical granuloma formation. Existence of immune cells in these lesions showed involvement of both humoral and cellular immunity in the site. The presence of different antigens in the root canal causes production o various antibodies and consequent immunological reactions. Different theories have been proposed on periapical cysts. The most valid of them is based onimmunologic response which can lead to tissue destruction due to immunological reactions.