Summary to Session 4

Having completed this final session of the course you should now be familiar with the basic features of a human being’s defences against pathogens. The first lines of defence are the physical barriers formed by the skin and secreted mucus, and the initial reaction to a breach of these defences is inflammation. We have introduced you to leukocytes, the key family of cells involved in the two types of immunity: innate and adaptive.

• Innate immunity involves the targeting of non-specific structures, known as PAMPS, on the surface of pathogens, and involves cytotoxic and phagocytic leukocytes.
• Adaptive immunity involves B cells and cytotoxic T cells, two types of leukocyte with receptors that bind to specific molecules on the surface of individual types of pathogen, as well as helper T cells that release signals to boost the immune response.

You have also learned that adaptive immune responses are boosted with repeated exposure to the pathogen due to the remarkable phenomenon of immunological memory. Importantly, immunological memory can be used by health care professionals to prevent disease through the process of vaccination. By exposing a person to an inactive form of a pathogen, that individual acquires an immunological memory of the pathogen. This means that if in future they become infected with the live pathogen they will launch a strong adaptive immune response and the pathogen is quickly destroyed.

As we have outlined, mass vaccination programs represent a key strategy in global health initiatives aimed at eradicating, or at least controlling, infectious diseases. Mass vaccination can be highly effective but, as you will now be aware, vaccine delivery is not straightforward; health workers often have to overcome ignorance and fear, as well as the logistical problems associated with so large a task.