The Lymphatic System and Immunity Explained

The Lymphatic System

The lymphatic system is a crucial part of the immune system, especially in the immune response.

• Lymphatic vessels allow accumulating lymph to carry and filter out pathogens through lymph nodes.
• The majority of lymphocytes are found in the lymphatic system. For example, T cells mature in the thymus while B cells mature in the bone marrow.

Humoral Immune System

The humoral response, which occurs in blood and lymph, primarily uses B cells to combat pathogens directly. B cells are triggered and activated by helper T cells before they can fight pathogens. When B cells encounter a pathogen they recognize, they engulf the foreign substance and display the antigens on their cell surface. Helper T cells then bind to these antigens, triggering the B cell to transform into a plasma cell. The plasma cell then releases antibodies that find pathogens with the corresponding antigen and mark them for destruction by phagocytosis.

Plasma cells that survive in the body for years are called memory cells. Memory cells enable a much faster response if the same pathogen infects the body again.

Cell-Mediated Immunity

The cell-mediated immune response leads to the destruction of body cells infected by viruses. This immune response mainly involves T cells, which need to be activated by antigens. However, different T cells demonstrate different responses.

• T cells are activated when they encounter the matching antigen on a leukocyte.
• Cytotoxic T cells make contact with the virus-infected cell and release lethal toxins to destroy the cell and the virus.
• Regulatory T cells help end the cell-mediated response and prevent T cells from accidentally attacking the body's own antigens.

Immunity

Memory B and T cells produced after an initial fight against an infection help the body quickly defend itself against another infection. This results in resistance to the pathogen, or immunity, which can be passive or active.

• Active immunity is a result of memory cells against a certain pathogen. Immunization is meant to build active immunity against a specific pathogen by purposely exposing the body to a mild version of the pathogen to trigger an immune response.
• Passive immunity is the transfer of antibodies to a person who has never been exposed to the pathogen.