Concept:
The lymphatic system helps in immunity, fluid balance, and filtration of lymph and blood.
Step 1: Understanding lymphatic organs.
Lymphatic organs include lymph nodes, spleen, thymus, and tonsils.
Step 2: Largest lymphatic organ.
The spleen is the largest lymphatic organ in the human body.
Step 3: Functions of spleen.
The spleen filters blood, destroys old RBCs, stores platelets, and helps in immune response.
Step 4: Checking other options.
Thymus is important for T-lymphocyte maturation.
Tonsils protect the throat region.
Lymph nodes filter lymph.
The spleen is the largest lymphatic organ.
\[
\boxed{\text{Spleen}}
\]