Objectives Genital tract infection of female mice with Chlamydia muridarum closely mimics C trachomatis acute genital tract infection in women. Aim of this study was to assess the predictivity of 11C-Choline Small Animal PET for the identification of reactive animals and their follow-up at several times after vaginal challenge.
Methods Chlamydiae were grown in LLC-MK2 cells, cultivated in Eagle's MEM and elementary bodies were purified from cells by sucrose-gradients density centrifugation. Animals used in this study were 10 female Balb/c mice, 6–8 weeks old. All the animals received 2.5 mg of medroxyprogesterone acetate intramuscular nine and 2 days prior the infection. Nine mice were infected by placing 106 IFUs of C muridarum into the vaginal vault. Infection was induced under Ketamine anaesthesia. As control, one animal was challenged with SPG. At 5, 10 and 20 days after challenge mice underwent a 11C-Choline PET, as follows: each animal was anaesthetised with Sevofluorane 3–5% oxygen 1 l/min and was injected with approximately 20 MBq of 11C-Choline, via the tail vein. The residual dose was measured to verify the effective dose injected. The animal was subsequently placed on the scanner bed in the prone position, after an uptake time of 5 min. Images were acquired with a small animal PET tomograph (GE, eXplore Vista DR) for a total acquisition time of 20 min. As the axial field of view was 4 cm, one bed position was sufficient to cover the whole body. Images were reconstructed iteratively (OSEM 2D) and read in three planes (axial, sagittal and coronal). The scan was considered positive if areas of increased Choline uptake were present at sites consistent with the site of inflammation. The standard uptake value (SUV) was calculated by measuring the concentration of the labelled tracer in the region of interest and correcting it for mice body weight and injected dose. Infection was monitored by culturing cervical-vaginal secretions 6, 11 and 21 days after infection.
Results At 5 days, the mean vaginal SUV (±SD) of the cases was 0.83±0.39, whereas the control showed a value of 0.278. At 10 and 20 days, SUVs of the cases were 0.94±0.25 and 1.17±0.21, respectively, whereas SUV of the control was 0.299 and 0.302, respectively. C muridarum was isolated from all the infected animals during the study period.
Conclusions These preliminary data indicate that 11C-Choline PET could be a promising technique to in vivo evaluate inflammatory response to Chlamydia infection.
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