Histochemical studies on microfilariae

Microfilariae belonging to the genera Brugia, Loa and Wuchereria have been stained by a wide variety of histochemical methods. The results are recorded in eight Tables. The sheath of the microfilaria contains polyanionic material, probably polysulphate, periodate reactive mucosubstance, sulphur-protein and complex lipids. The fluid within the sheath is also polyanionic. The cuticle of the microfilaria is stabilized by disulphide bonds possibly in a collagen but it was not possible to demonstrate collagen by staining. The cuticle also contains a periodate reactive G mucosubstance and complex lipids. The annular grooves of the cuticle also contain a periodate unreactive mucosubstance. Certain areas of the cuticle, around the excretory pore, the pores of the Schwanzgebilde, and the cephalic structures - oral ring, hook and spines - are hardened by deposition of a keratinous scleroprotein. Some reactions of the cuticle may be masked by the presence of basic protein. The excretory vesicle contains polyanionic material but there was no clear evidence that the polyanionic material within the fluid in the sheath came from the excretory vesicle. The excretory vesicle, the anal vesicle and the subcuticular cells contain periodate reactive G mucosubstance. Most RNA staining was found in the excretory vesicle, the excretory cell, the anal vesicle, the rectal cells and the G cell. The pharyngeal thread, the Innenkörper, the rectal cells and the anal vesicle represent the modified gut of this first stage larva. The pharyngeal thread appears to consist largely of a protein-mucosubstance complex that can be unmasked by oxidation. The Innenkörper contains a basic protein and acidic mucosubstance, possibly sialomucin, complex that can be unmasked by adjusting the electrolyte concentration of the staining media. The relevance of some of these techniques in the analysis of possibly unique invertebrate structures is discussed briefly. We thank Dr D. A. Denham, Mr P. R. N. Pester and Dr T. Ponnudurai in particular, and many other correspondents, for supplying us with microfilariae for staining. This work was supported by a grant from the Medical Research Council of Great Britain.