Regulation of Plasmodium sporozoite motility by formulation components

Abstract

Background The protective efficacy of the most promising malaria whole-parasite based vaccine candidates critically depends on the parasite’s potential to migrate in the human host. Key components of the parasite motility machinery (e.g. adhesive proteins, actin/myosin-based motor, geometrical properties) have been identified, however the regulation of this machinery is an unknown process. Methods In vitro microscopic live imaging of parasites in different formulations was performed and analysed, with the quantitative analysis software SMOOT In vitro , their motility; their adherence capacity, movement pattern and velocity during forward locomotion. Results SMOOT In vitro enabled the detailed analysis of the regulation of the motility machinery of Plasmodium berghei in response to specific (macro)molecules in the formulation. Albumin acted as an essential supplement to induce parasite attachment and movement. Glucose, salts and other whole serum components further increased the attachment rate and regulated the velocity of the movement. Conclusions Based on the findings can be concluded that a complex interplay of albumin, glucose and certain salts and amino acids regulates parasite motility. Insights in parasite motility regulation by supplements in solution potentially provide a way to optimize the whole-parasite malaria vaccine formulation. Electronic supplementary material The online version of this article (10.1186/s12936-019-2794-y) contains supplementary material, which is available to authorized users.

Clustering and erratic movement patterns of syringe-injected versus mosquito-inoculated malaria sporozoites underlie decreased infectivity

“…Sporozoite velocity fluctuated along tracks (visualized by color-coding in Fig. 5A), also in line with our earlier findings (14,17). Plotting the average track-velocities revealed a distribution that could be described with a mixture of two normal distributions (Fig.…”

“…Our ex vivo set-up combined with spinning-disk confocal microscopy and sporozoite tracking software enabled 1) the visualization of (the sporozoite distribution throughout) the whole inoculation and injection site (up to 100 mm 2 ), whereas up to now only one field of view (<0.5 mm 2 ) was visualized during in vivo live imaging (13,16,35), 2) the visualization of morphological tissue deformation as a result of pressure of fluid injection, previously acknowledged as an important parameter regarding transdermal drug delivery (36)(37)(38), but not yet visualized at a micron level resolution and 3) a multidimensional analysis of sporozoite motility unveiling an remarkable interplay between motility parameters which were up to now only studied independently (15)(16)(17). Further research is needed to study the role of other potential contributors not accounted for in this imaging study, such as their preprocessing (manual extraction from salivary glands in culture medium instead of saliva (14,39,40)). Our quantitative assessment of parameters affecting sporozoite migration both indicates that engineering solutions should be explored that can better mimic mosquito inoculation as well as provides a readout needed to assess the potential of the suggested engineering solutions.…”

“…Conversely, the slower erratic movement of syr SPZ is most likely caused by the altered physical space as a consequence of liquid injection pressure. Sporozoite movement is strongly guided by their three-dimensional environment; without any confinement, sporozoites in vitro display a continuous, preferential counter-clockwise movement pattern (14,25), while in vivo, skin structure redirects sporozoites to display much more complex patterns (15,17). The role of physical confinement has been further supported by experiments whereby micropatterned in vitro environments were created that could induce specific movement patterns of sporozoites (26).…”

“…The motility of the sporozoites was analysed using SMOOTmouse skin, an in-house developed software program, written in the MATLAB programming environment (MathWorks). This tool is an adapted version of the SMOOThuman skin (12,17) and SMOOTIn vitro (14) tools previously described. Via…”

“…The subsequent development of fluorophore-expressing sporozoites and a sporozoite fluorescent labelling approach has allowed for more detailed microscopic studies on the motility of individual sporozoites, both in vitro and in skin (11,12). Moreover, automated analysis of sporozoite motility now provides a platform to quantitatively study sporozoite motility under different conditions (13)(14)(15)(16)(17).…”