Question

The interactions between pathogens and their mammalian hosts are played out on co-evolutionary battlegrounds. Discuss this statement by explaining:
a) Why humans are constantly susceptible to infection despite the evolution of complex innate and adaptive immune responses and,
b) How pathogens, and the molecules they produce, interact with macrophages to cause disease and can sometimes be exploited for therapeutic benefit.

Answer 1

a. There are many types of infections which means many types of infecting agents ranging from varieties of viruses, bacteria, protozoa, helminths, fungi etc. Apart from that, there are many pollutants which keep on entering our body every second. Though our immune system has evolved to fight a variety of infections still the number and varieties of pathogens keep on increasing. Moreover, existing varieties of viruses are quite capable of changing their coats i.e changing their antigens. This has quite pressurized the immune system to adapt according to changing pathogens and their coats.

b. In their role as phagocytic immune cell macrophages are responsible for engulfing pathogens to destroy them. Some pathogens subvert this process and instead live inside the macrophage. This provides an environment in which the pathogen is hidden from the immune system and allows it to replicate. Sometimes such pathogens are used for vaccination purposes by changing their antigenic properties i,e weakening them, thus they are also used as therapeutic agents.