VARIANT CYSTEINE-RICH SURFACE-PROTEINS OF GIARDIA ISOLATES FROM HUMANAND ANIMAL SOURCES

Cloned Giardia isolates obtained from a sheep, a calf, and a human pos sessed a major membrane protein that showed marked intraspecific varia tions in size as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis following surface biotinylation and radioiodinati on. Metabolic labeling with [S-35]cysteine and electrophoretic analysi s also revealed for each cloned isolate a predominant protein that cor responded in size to the major surface protein demonstrated by surface labeling techniques. Immunoprecipitation studies with a polyclonal an tiserum specifically directed against the 90-kDa major cysteine-rich p rotein purified from a subclone of the sheep isolate (02-4A1) showed t hat the cysteine-rich protein and the major surface protein are identi cal. The surface location of the antigen was further corroborated by t he reaction of fluorescence-labeled antibodies raised against the 90-k Da 02-4A1 cysteine-rich protein with the entire surface of live tropho zoites of the homologous clone. The ability of the cloned Giardia isol ates to undergo variations of their cysteine-rich surface protein (CRI SP) was demonstrated by the spontaneous appearance of new CRISPs in cl onally derived populations during prolonged in vitro culturing and in cultures of the 02-4A1 clone that had survived treatment with the cyto toxic anti-90-kDa CRISP antiserum specific for the surface antigen of this clone. The surviving progeny were devoid of the original CRISP, a s judged by resistance to the immune serum. Subsequent cysteine metabo lic labeling of the recloned surviving trophozoites demonstrated a lar ge number of new variants, each expressing a single CRISP that varied significantly in molecular weight from those in the different cloned l ines. These studies suggest that the presence of CRISPs and their vari ations are not restricted to Giardia isolates obtained from humans but are universal phenomena among the Giardia duodenalis types of organis ms.