Biomedical Engineering Reference
In-Depth Information
the. host. red. blood. cell,. the. parasite. begins. to. modify. the. structural,. and. correspond-
ingly. the. biomechanical,. properties. of. the. cell.. The. growing. trophozoite. stage. exports.
a. range. of. proteins. to. the. erythrocytic. cytoskeleton. and. membrane.. In. the. case. of. the.
deadly.
P. falciparum
,.a.protein.called.knob-associated.histidine.rich.protein.(KAHRP).is.
exported.to.the.red.cell.cytoskeleton.within.22.h.of.the.parasite.invading.the.host.cell.
3
.
KAHRP. cross-links. the. actin. and. spectrin. of. the. cytoskeleton,. both. reducing. elastic-
ity. and. causing. knob-like. excrescences. to. appear. on. the. cell. surface.. The. knobs. of.
P.
falciparum
.and.their.associated.proteins.anchor.and.expose.an.array.of.important.adhe-
sion. proteins. known. as.
P. falciparum
. erythrocyte. membrane. protein. 1. (P
f
EMP1).. The.
P
f
EMP1-covered.knobs.of.the.
P. falciparum
.infected.red.blood.cell.(IRBC).interact.with.
a.range.of.surface.proteins.expressed.on.host.endothelial.cells,.which.stick.the.infected.
cells.to.the.blood.vessel.wall.to.avoid.splenic.clearance,.under.considerable.shear.low.
stresses.(up.to.1 Pa).
4
.Unfortunately,.the.rigid.sticky.IRBCs.of.
P. falciparum
.readily.block.
the.microvasculature.of.important.organs.such.as.the.brain,.leading.to.severe.diseases..
Despite.numerous.reports.of.severe.diseases.in.
P. vivax
.and.
P. malariae,
.few.studies.have.
investigated. nanostructures. on. the. surface. of. these. non-
P.
.
falciparum
. species.. Another.
important.gap.in.our.knowledge.results.from.most.structural.studies.on.the.knobs.of.
P.
falciparum
IRBCs.relying.on.culture-adapted.laboratory.clones.from.in.vitro.or.primate.
models..Little.has.been.done.to.describe.these.features.in.ield.isolates.or.correlate.them.
with.a.carefully.deined.clinical.phenotype.
15.3 TraditionalMethodstoInvestigatetheSurface
MorphologyofMalaria-InfectedRedCells
Since. the. 1950s,. scanning. electron. microscopy. (SEM). and. transmission. electron. micros-
copy.(TEM).have.been.used.by.numerous.investigators.to.examine.morphological.changes.
to.the.malaria.IRBCs.
5
.Both.of.these.electron.gun-based.methods.provide.an.unparalleled.
tool.to.investigate.in.high.resolution.subnanometer.changes.to.the.surface.of.the.red.cell.
(Figure 15.1).
Although.TEM.has.the.advantage.of.observing.nano-ultrastructural.details.inside.the.
cell. at. extremely. high. resolution,. since. the. cells. have. to. be. sliced. into. ultra-thin. pieces,.
it. does. not. allow. us. to. completely. study. the. morphological. features. on. the. cell. surface,.
such.as.the.knob's.full.size,.density,.etc.,.in.three.dimensions..Alternatively,.SEM.is.able.
to. produce. impressive. three-dimensional. (3D). images. of. the. surface. of. the. IRBC. mem-
brane;.however,.it.does.not.allow.accurate.quantitative.measurements.of.the.nanofeature,.
such.as.knob.height.and.density,.and.more.importantly,.SEM.could.not.see.through.the.
surface.to.identify.the.parasite.developmental.stages..Both.TEM.and.SEM.methodologies.
require. extensive. sample. preparation. and. involve. numerous. ixing. and. slicing/coating.
procedures.that.may.severely.alter.the.shape.of.the.IRBC.surface,.obscuring.ine.changes.
or. creating. artifacts.. This. has. led. to. some. disagreements. in. the. literature. regarding. the.
presence.of.knobs.and.other.nanofeatures.in.non-
P. falciparum
spp..For.example,.data.from.
past. studies. on.
P. malariae
. IRBCs. using. TEM. disagree:. one. study. by. Mackenstedt. et al.
7
.
suggested. no. knobs. but. numerous. caveolae. (caveolae. are. pleomorphic. invaginations. on.
the. surface. membranes. of. cells),. while. Atkinson. et. al.
8
. showed. the. presence. of. knobs..
Another.important.problem.confronting.past.studies.is.that.most.of.them.were.carried.out.
on.clinical.isolates.that.were.not.conirmed.by.molecular.speciation.techniques..As.optical.
