As lymph nodes filter out what substances, they swell?

Lymph nodes play a crucial role in the immune system by filtering lymph fluid and trapping pathogens. When lymph nodes encounter harmful microorganisms, such as bacteria, they initiate an immune response. This response includes the activation and multiplication of lymphocytes—white blood cells that help the body fight infections. As these immune cells accumulate in the lymph nodes, they cause the nodes to swell, a response indicative of an active immune response.

While viruses, toxins, and allergens can also provoke an immune response, the swelling of lymph nodes is most commonly associated with bacterial infections as the body actively responds to these invasions. Bacterial presence often leads to a more pronounced immune response, resulting in noticeable enlargement of the lymph nodes as they work to filter and eliminate these pathogens.