Experimental infection and protection against ... - TI Pharma

200 Chapter 10
by hand-dissection. Salivary glands were collected in RPMI-1640 medium (Gibco)
and homogenized in a custom glass grinder. Free sporozoites were counted in a
Bürker-Türk counting chamber using phase-contrast microscopy. PfSpz were
cryopreserved at 16x10 6 /ml in 15% glycerol/PBS in aliquots for use in individual
stimulation assays. Sporozoites that had undergone one freeze-thaw cycle were
morphologically intact, but no longer able to glide (assay described in [16], using
a FITC-3SP2 conjugated antibody). Salivary glands from an equal number of
uninfected mosquitoes were used as a background control.
NF54 strain P. falciparum asexual blood-stage parasites (PfRBC), regularly
screened for mycoplasma contamination, were grown in RPMI-1640 medium
containing 10% human A+ serum at 5% haematocrit in a semi-automated
suspension culture system, in the absence of antibiotics and in an atmosphere
containing 3% CO2 and 4% O2. For in vitro stimulation experiments,
asynchronous asexual-stage cultures of NF54 strain parasites were harvested at
a parasitemia of approximately 5-10% and mature asexual stages purified by
centrifugation on a 27% and 63% Percoll density gradient [17]. This purification
step results in preparations of 80-90% parasitemia, consisting of more than 95%
schizonts/mature trophozoites. PfRBC were washed twice in PBS and
cryopreserved at 150x10 6 /mL in 15% glycerol/PBS in aliquots for use in
individual stimulation assays. Mock-cultured uninfected erythrocytes (uRBC)
were obtained similarly and served as control.
Stimulation assay and staining for flow cytometry
After thawing, cells were stimulated with either cryopreserved NF54 PfRBC (as
previously described [9]) at a final concentration of 5*10 6 /ml or cryopreserved
PfSpz at a concentration of 4*10 5 /ml for 24 hours. Uninfected red blood cells
(uRBC, 5*10 6 /ml) and uninfected mosquito salivary glands (MSG) preparations
dissected from equal numbers of uninfected mosquitoes, respectively, were
used as negative controls. For cell stimulations with sporozoites/MSG 0.8 µl/ml
CD28/CD49d reagent (BD) was added to the culture as a co-stimulant.
PMA/ionomycin stimulation (50ng/ml and 1µg/ml respectively, Sigma-Aldrich)
was used as positive control and added four hours before harvest. Brefeldin A
(final concentration 10μg/mL) was added to all wells four hours prior to harvest.
For staining procedures, PBMC were transferred to a 96 V-wells micro-titre plate
(500,000 cells/well), washed and incubated with LIVE/DEAD® cell stain kit Aqua
(Invitrogen, Carlsbad, CA, USA) for 30 min at 4°C. Cells were washed in FACS
buffer (PBS containing 0.5% Bovine Serum Albumin, Sigma-Aldrich Co.), and