Specific mechanisms (internal defenses)
If the primary barriers (physical, mechanical, chemical and microbiological) and the secondary ones (phagocytes) are overcome, the microorganisms can spread throughout the body, generalizing the infection.
The adaptive immune system is the body's third defensive barrier and is more powerful than phagocytosis. This response is specific, it only acts against the identified pathogen (by surface antigens) and eliminates it.
The immune response is carried out by lymphocytes, in two ways:
- Cell response. Directly, performed by T lymphocytes.
- Humoral response. Indirectly, with antibodies synthesized by B lymphocytes.
Another characteristic of this response is that it has immunological memory. The immune system produces memory lymphocytes that remember each antigen after its first contact (primary response). If there is another subsequent contact with that antigen, the response (secondary response) is much more rapid and intense.
The immune system has immunological tolerance, which is why it can distinguish its own molecules from those of others and does not attack the cells of the body's tissues. Sometimes failures occur and cause autoimmune diseases.
The specific immune response is carried out according to these phases:
- Recognition of the antigen.
- Directly: Lymphocyte membrane receptors detect the antigen.
- By means of antigen-presenting cells: they engulf the antigens and leave some fragments on their surface.
- Activation of lymphocytes.
- Once the antigen is recognized, the lymphocytes reproduce and activate.
- Triggering of the immune response.