Monday, April 02, 2012

Schistosoma hematobium- Fooling around with immunity

Welcome back.
          
          Talking always about new research has got a problem. The best understood among them is loss of previous basic knowledge. Well, if you don't believe me then, check it up yourself. Meanwhile let me tell you something that i know for sometime now.

          Parasites are one of the interesting creatures. And i must make a statement here. They are one of the underestimated pathogens and less studied too. Heard of Schistosoma hematobium? I always remember them as most romantic parasites, the male and female always in arms of each other. For a newcomer to this area i have put up a brief summary here along with his kins- mansoni and japonicum

Feature
S hematobium
S mansoni
S japonicum
Male
Covered with minute tuberculation
Covered with conspicuous tuberculation
Covered with minute acuminate spine
Female Ovary
Posterior 1/3rd of body
Anterior half of body
Middle of body
Eggs discharged in
Urine
Faeces
Faeces
Infective form
Fork-tailed cercariae that can penetrate intact skin
Habitat
Veins of vesical and pelvic plexus
Mesentric vein draining sigmoido-rectal region
Mesentric vein draining Ileo- cecal regions
Definitive Host
Man
Man
Man and Domsetic animals
Intermediate Host
Bulinus Species
Biomphalaria Sp
Oncomelania Sp

Table 1: Features of S hematobium and related species.


For a ppt view of Schistosoma and other treamtodes click here


           So, those of you who know about this pathogen, you would also know that this parasite lives in the venous plexus. Thats just equivalent to standing right in front of your enemy army alone and waving saying "hey, look am here". So how does this worm escape wrath of immunity?


Photo 1: Schistosoma (Taken from Science Photo library)

          Hmmm. Let me teach you a magic. If you are to become invisible do u know what the magicians do? Simple. Wear a black suite and stand in front of a black background. The same can be achieved with any color combination. The principle is the color should be the same, so that they blend into the background. Why am I telling u these tricks? Just to tell you this is what the worm does.

          Schistosomes express a bunch of integral membrane proteins, called tetraspanins (TSPs), in the outer surface membranes of the tegument. These tegument are characterized by the conserved structure of four hydrophobic transmembrane domains, a small and large extracellular loop, an interconnecting intracellular loop, and cytoplasmic amino- and carboxyl- termini.


Fig 1: Tetraspanin structure, For source click here

          This TSP can mask the inner parasitic antigens, by pasting and displaying the hosts own antigen which is circulating in blood. Just like standing with black cloths on a black background, the immune system is easily fooled by this trick. And the parasite just dances around in the plexus happily continuing its life cycle.

Further reading:

1. Yanyan Jiang etal. Identification and characterization of six novel tetraspanins from Schistosoma japonicum. Parasites & Vectors 2011, 4:190.

2. Tran MH, Freitas TC, Cooper L, Gaze S, Gatton ML, et al. (2010) Suppression of mRNAs Encoding Tegument Tetraspanins from Schistosoma mansoni Results in Impaired Tegument Turnover. PLoS Pathog 6(4): e1000840.

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