ABSTRACTCysts ofGiardia lambliaandEntamoeba histolyticaand oocysts ofToxoplasma gondiiandCryptosporidium parvumare the infectious and sometimes diagnostic forms of these parasites. To discover the structural components of cyst and oocyst walls, we have developed strategies based upon a few simple assumptions. Briefly, the most abundant wall proteins are identified by monoclonal antibodies or mass spectrometry. Structural components include a sugar polysaccharide (chitin forEntamoeba, β-1,3-linked glucose forToxoplasma, and β-1,3-linked GalNAc forGiardia) and/or acid-fast lipids (ToxoplasmaandCryptosporidium). BecauseEntamoebacysts andToxoplasmaoocysts are difficult to obtain, studies of walls of nonhuman pathogens (E. invadensandEimeria, respectively) accelerate discovery. Biochemical methods to dissect fungal walls work well for cyst and oocyst walls, although the results are often unexpected. For example, echinocandins, which inhibit glucan synthases and kill fungi, arrest the development of oocyst walls and block their release into the intestinal lumen.Candidawalls are coated with mannans, whileEntamoebacysts are coated in a dextran-like glucose polymer. Models for cyst and oocyst walls derive from their structural components and organization within the wall. Cyst walls are composed of chitin fibrils and lectins that bind chitin (Entamoeba) or fibrils of the β-1,3-GalNAc polymer and lectins that bind the polymer (Giardia). Oocyst walls ofToxoplasmahave two distinct layers that resemble those of fungi (β-1,3-glucan in the inner layer) or mycobacteria (acid-fast lipids in the outer layer). Oocyst walls ofCryptosporidiumhave a rigid bilayer of acid-fast lipids and inner layer of oocyst wall proteins.
Identification of an immunogenic protein of Giardia lamblia using monoclonal antibodies generated from infected mice
