Which of the following serve(s) to trap the micro-organisms that get into the tissue fluid?

The lymph nodes are small solid structures located at different points along the lymphatic system. They serve to trap the microorganisms or other antigens, which happen to get into the lymph and tissue fluid. Antigens trapped in the lymph nodes are responsible for the activation of lymphocytes present there and cause the immune response.

The spleen acts as a filter of the blood by trapping blood-borne microorganisms.