Rosetting of Plasmodium falciparum required multiple components of the uninfected erythrocytes.

The mechanism of rosette formation of uninfected erythrocytes with Plasmodium falciparum-infected erythrocytes is rarely described. In this study, rosetting of uninfected normal erythrocytes with infected erythrocytes significantly reduced after treatment of the uninfected erythrocytes with neuraminidase. In contrast, the rosetting property of the infected erythrocytes was abolished by trypsinization but not by neuraminidase. The in vitro rosetting model showed that uninfected thalassemic erythrocytes poorly formed rosettes with infected normal erythrocytes when compared with normal erythrocytes of the same blood group. A rosetting parasite clone showed significant reduction in rosetting with thalassemic erythrocytes of all blood groups, however, this reduction was not obvious when the wild P. falciparum isolates were studied. These results suggest that while parasites from a single clone can rosette with uninfected erythrocytes via carbohydrate component, there is more than one type of receptor on uninfected erythrocytes involved in rosette formation with the heterogeneous populations of the wild P. falciparum isolates.

Induction of protective immunity against infection by Angiostrongylus cantonensis in rats.

Attempts were made to induce acquired immunity against Angiostrongylus cantonensis infection by immunizing rats with somatic (L3S) and metabolic (L3ES) antigens from third-stage larvae and with somatic antigen from adult female worms (FACE) via either a combined intraperitoneal and oral (IP-OR-OR) or subcutaneous (SC-SC-SC) route. The most effective mean in inducing protection was the administration of L3S by the IP-OR-OR route, as judged from reduced mortality, prolonged survival periods and/or reduced worm burdens. Such a protocol reduced mortality to below 20% of the unimmunized controls. The worm burden of the L3S-immunized rats was only about 25% of the control value and the survival period was at least double. However, judging from gross morphology, the absence of stunted growth and unimpaired ficundity of the worms that developed into adult stage, it appears that those worms that survived had normal development. The latter observation is in contrast to that noted with FACE immunization which seemed to affect also the growth and development of worms that survived into adult stage.

Analysis of antigens from different developmental stages of Angiostrongylus cantonensis.

Protein profiles of somatic extracts from different developmental stages and excretory and secretory products of third-state larvae of Angiostrongylus cantonensis were analyzed and characterized by polyacrylamide gel electrophoresis in sodium dodecyl sulfate under both reduced and unreduced conditions. Immunological identification of common and stage-specific antigens was determined by radioimmunoprecipitation using chronically infected rat serum and antisera from rats immunized with somatic extracts of third-stage larvae and adult female worms. The somatic extracts of first-and third-stage larvae and of adult worms were found to be highly complex, each consisting of more than 20 different peptides with molecular weights varying from higher than 130,000 to 8,200 daltons. Most proteins were composed of single polypeptide chains. Polypeptides with molecular weights of 80,000, 39,500 and 22,000 daltons were present in more than one developmental stages and were antigenically related. Those with molecular weight of 15,500 dalton, was present primarily in L3S and its possible usefulness in immunodiagnosis of infection that occurs in man was discussed.