Adaptive immunity can be divided into cell-mediated immunity and humoral (fluid-based) immunity. The adaptive immune response is kicked off by so-called helper T cells. In the immune reaction antigen-presenting cells (APC cells, part of innate immunity) mark and eat the pathogen. APC cells then move to lymph nodes where helper T cells launch the actual adaptive immunity response.
When a new pathogen is being encountered for the first time, the reaction is slow and can take up to two weeks. When the pathogen is previously known, the defense reaction begins within a few days. Vaccines are used to introduce pathogens to the immune system in advance. If the pathogen has mutated, the immune system may no longer recognize it as the same disease. This is why it is possible to catch the flu again and again. Some pathogens such as human papilloma viruses (HPV) and herpesviruses also have the ability to hide from the immune system.
Cell-mediated immunity is a part of adaptive immunity that is based on lymphocytic function. It focuses primarily on fighting the pathogens multiplying within the body’s own cells. These include viruses, mycobacteria and protozoa. Unlike humoral immunity, cell-mediated immunity does not involve antibodies.
Like cell-mediated immunity, humoral immunity is a part of adaptive immunity. It is responsible for fending off pathogens that occur outside cells. These include various bacteria and toxins secreted by this bacteria. The defense mechanisms of humoral immunity are the responsibility of the antibodies circulating in the blood and on the surface of mucous membranes, as well as cytokine and complement systems.