Localisation of internal antigens of Plasmodium falciparum using monoclonal antibodies and colloidal gold

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Abstract
By the examination of several defined malarial antigens, we have demonstrated the necessity for etching pretreatments to be used in conjunction with post-embedding immunolabelling of LR White-embedded parasite material. In general, etching procedures markedly enhanced immunolabelling of the various antigens, while in some cases etching was essential for obtaining positive immunolabelling. Of the etching pretreatments evaluated, a combination of an alcoholic solution of sodium hydroxide followed by sodium metaperiodate gave optimal labelling with minimal background. A number of fixation regimes were also compared for their applicability to immunolabelling of malaria-infected erythrocytes. Generally, fixation with low concentrations of glutaraldehyde was found to be appropriate. We have also successfully used paraformaldehyde fixation coupled with etching to localise a rhoptry-associated antigen, which is presumably sensitive to glutaraldehyde fixation. Due to the high specificity of monoclonal antibodies, however, different fixation regimes may need to be considered for various combinations of antigen and antibody.