Four antibodies used routinely in-house for the assessment of antiglobulin reagents (anti-Fyb, anti-Jka, anti-S) were tested in parallel using tube and antiglobulin 'gel-test' low ionic strength antiglobulin techniques. In the latter the red cells are centrifuged following incubation through a dextran matrix incorporating an anti-human globulin reagent. The results show that the antiglobulin 'gel-test' was less sensitive than the tube technique in the detection of these difficult antibodies.

Plasmodium falciparum merozoites have an array of 2-3 subpellicular microtubules, designated f-MAST. We have previously shown that colchicine inhibits merozoite invasion of erythrocytes, indicating a microtubular involvement in this process. Colchicine inhibition of invasion was reduced by the Taxol-stabilization of merozoite microtubules prior to colchicine exposure. Immunofluorescence assays showed that the number and length of f-MASTs were reduced in colchicine-treated merozoites, confirming that microtubules were the target of colchicine inhibition. The dinitroaniline drugs, trifluralin and pendimethalin, were shown by immunofluorescence to depolymerize the f-MAST and both drugs were inhibitory in invasion assays. These results demonstrate that the integrity of the f-MAST is important for successful invasion. Fluorescence imaging demonstrated the alignment of mitochondria to f-MAST, suggesting that mitochondrial transport might be perturbed in merozoites with disorganized f-MAST. Depolymerizing mt in late-stage schizonts did not affect the allocation of mitochondria to merozoites.

The genome of the malaria parasite, Plasmodium falciparum, contains a myosin gene sequence, which bears a close homology to one of the myosin genes found in another apicomplexan parasite, Toxoplasma gondii. A polyclonal antibody was generated against an expressed polypeptide of molecular mass 27,000, based on part of the deduced sequence of this myosin. The antibody reacted with the cognate antigen and with a component of the total parasite protein on immunoblots, but not with vertebrate striated or smooth muscle myosins. It did, however, recognise two components in the cellular protein of Toxoplasma gondii. The antibody was used to investigate stage-specificity of expression of the myosin (here designated Pf-myo1) in P. falciparum. The results showed that the protein is synthesised in mature schizonts and is present in merozoites, but vanishes after the parasite enters the red cell. Pf-myo1 was found to be largely, though not entirely, associated with the particulate parasite cell fraction and is thus presumably mainly membrane bound. It was not solubilised by media that would be expected to dissociate actomyosin or myosin filaments, or by non-ionic detergent. Immunofluorescence revealed that in the merozoite and mature schizont Pf-myo1 is predominantly located around the periphery of the cell. Immuno-gold electron microscopy also showed the presence of the myosin around almost the entire parasite periphery, and especially in the region surrounding the apical prominence. Labelling was concentrated under the plasma membrane but was not seen in the apical prominence itself. This suggests that Pf-myo1 is associated with the plasma membrane or with the outer membrane of the subplasmalemmal cisterna, which forms a lining to the plasma membrane, with a gap at the apical prominence. The results lead to a conjectural model of the invasion mechanism.