Thursday, February 20, 2014

Defense Evasion: Molecular Mimicry

Parasites, like ninjas, need to come up with intuitive ways to evade their targets defenses.  Parasites are organisms that rely on a host in order to reproduce and survive. The ability of a parasite to withstand the onslaught of their host’s defenses, such as the immune system, is a critical factor in determining life or death.  Natural selection has given parasites multiple ways of avoiding the host defense.  Some of the survival mechanisms  parasites utilize include hiding in areas of the host where the immune response is overlooked, suppressing the immune system in order for easier invasion, and forming a protective cyst. [1] In addition to these avoidance mechanisms, parasites have clever method  to cloak themselves from  phagocytic cells of the host. These parasites can produce compounds in order to disguise itself as part of the host. This sneaky tactic, molecular mimicry is an ingenious method of protection from a hosts immune system. [1]

Hide and Seek
 Parasites rely on molecular mimicry in order to stay hidden from dangerous phagocytes of the immune system. The basic premise of this mechanism  is for the parasite to produce a cellular component that can be identified by the host immune system as its own.[1] This stealthily enables the parasite to hide its antigen characteristics, and this lowers the risk of recognition by phagocytes. [1] This molecular deception is used by various parasites to enhance their chance of survival in hosts.  For example, the intracellular parasite, Neisseria meningitids, which causes meningitis, uses molecular mimicry to protect itself from the hosts immune system. [5] Neisseria is able to avoid the antibody mediated immune system response by producing a protein that binds to factor H of the immune system. [5] Factor H  binds to normal cells for autoimmune protection. [5] This prevents the healthy cell of the host from being attacked by its own immune system. [5] By being able to produce a protein that binds to factor H, Neisseria, is able to hide and gain similar protection just like normal cells.[5]  As a result, Neisseria, is able to hide among the cells without facing destruction.

We Are Cloaked!

The blood fluke, Schistosoma mansoni, is a small worm that infects millions of people with the chronic illness known as intestinal schistosomiasis. [4] The fluke goes through different stages of development in order to reach full maturity. [4] Before mansoni can infect humans, it uses snails as an intermediate host. [4] The snail provides a place for the fluke to mature on its journey to reach its definite host. [4] The problem that arises during this period of growth is the snail's immune system, and in order to survive, mansoni must use the power of molecular mimicry.[4] The immune system of a snail is comprised of molecules called lectins, and these function  in the recognition of various molecule such as carbohydrates and sugars. [4] The lectins help seek out foreign particles in the snails immune system and stimulate an immune response. [4]  In order to counteract this detection system, the  fluke possess sugars that are already present in snails, and this makes it very difficult for the lectins to recognize the flukes’ presence as foreign.[4] By using molecular mimicry the blood fluke is to cloak itself while developing in the intermediate host without any interruption. Molecular mimicry makes it possible for parasites to sustain themselves in the unforgiving environment of the host. 
As a result, molecular mimicry gives parasites a fighting chance against the deadly defenses found in many host organisms. Out of all the methods that  parasites can utilize to stay alive in the host, molecular mimicry is a devious approach to achieving a higher chance of survival. 


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