lymph nodes: filter harmful particles that are throughout the body
Thymus: a lymphoid organ situated in the neck of vertebrates that produces T cells for the immune system
The thymus serves a vital role in the training and development of T-lymphocytes or T cells, an extremely important type of white blood cell.
Spleen: an abdominal organ involved in the production and removal of blood cells in most vertebrates and forming part of the immune system.
The spleen acts as a filter for blood as part of the immune system.