Microfilarial sheaths of Litomosoides carinii were isolated and extracted with 2% sodium dodecyl sulfate (SDS) and 5% 2-mercaptoethanol (2ME). Extraction with SDS alone did not alter the ultrastructure of the sheaths and yielded five polypeptides (27-67 kDa) that were not recognized by antibodies of infected hosts but reacted with antibodies to host-serum proteins. 2ME treatment caused partial solubilization of the sheaths (45% as determined by amino acid analysis), which could be further improved by combining 2ME with SDS. The remainder showed filamentous/threadlike structures on electron microscopic examination. As compared with whole sheaths, the insoluble proportion was markedly enriched in alanine and cysteine but contained less galactosamine, serine, and threonine. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of 2ME/SDS-extractable components showed 12-16 bands of 14- greater than 120 kDa. A predominant component had an apparent molecular mass of 22 kDa. Two bands (42 and 120 kDa) could be stained with Coomassie blue but showed "negative" staining when gels were stained with silver. Several components (but not the 22-kDa polypeptide) bore phosphocholine epitopes. Apart from the negatively staining bands, most of the 2ME-soluble sheath components were recognized by antibodies of L. carinii-infected Mastomys coucha. Except for several polypeptides that had been unspecifically recognized by IgM, the antibody response to sheath components started at the end of the prepatent period.

Burgia malayi and B. pahangi microfilariae were isolated from the blood of infected Mastomys natalensis, and were exsheathed by freezing, thawing and agitation. Pure sheaths were obtained by a filtration procedure. The sheaths were found to contain about 95 mol% of amino acids, with proline, glutamic acid/glutamine, alanine, cysteine/cystine and glycine being the major components, and 5 mol% of carbohydrates, notably (N-acetyl)galactosamine, but no (N-acetyl)glucosamine.

The major glycoprotein of the sheath of Litomosoides carinii microfilariae (gp22) was analysed for its amino acid and amino sugar composition. It is rich in proline, glutamine/glutamic acid and glycine and contains (N-acetyl)galactosamine. The N-terminal amino acid sequence was determined up to position 37. It consists of a group of 6 repeats of the pentapeptide sequence methionine-glycine-proline-glutamine-proline with two minor modifications in repeats 3-6, while the first two repeats follow the general pattern more loosely. Identical N-terminal amino acid sequences were found in at least two other sheath polypeptides (33 kDa, 39 kDa). Antisera prepared against 3 overlapping synthetic peptides corresponding to the amino terminus of gp22 recognized different epitopes. They all reacted with identical patterns of sheath polypeptides. The antisera failed to recognize antigens of 4th-stage larvae of L. carinii. In contrast, cross-reacting epitopes were detected in other parasite stages. Antisera reacted with material surrounding embryos and microfilariae in the uterus of females, and caused patchy fluorescence on the sheath of blood-derived and in vitro-released microfilariae.

A method is described for the isolation of pure, chemically intact sheaths of blood microfilariae of Litomosoides carinii. Microfilariae were isolated according to standard techniques. Exsheathment was performed by freezing-thawing-shaking procedures, repeated 5-10 times, i.e., larvae were frozen in liquid nitrogen, thawed at room temperature, and shaken vigorously for 5 s. Exsheathment rates were about 50%. Sheaths were separated from ensheathed and exsheathed microfilariae and microfilariae fragments by filtration through a polycarbonate filter (2 micron pore size). The achievable yield (about 15% of the sheaths of a batch of microfilariae) was approximately 1 microgram of sheaths per 10(6) microfilariae.

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