Given the task definition and input, reply with output. In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

This organ produces a tetrapeptide, which bonds to macrophage receptors, and is known as tuftsin. The sinusoids of one portion of this organ contain blood and a reserve of monocytes which can be utilized in the case of hemorrhagic shock. The other major portion of this organ contains Malphigian corpsules and synthesizes antibodies. Located in the abdominal region and consisting of red and white pulp, for 10 points, name this organ part of the lymphatic system that helps to filter and clean the blood.
Social Science