الفهرس 
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Abstract
7. Summary
Toxoplasmosis is an infectious disease caused by an obligate intracellular parasitic protozoan, Toxoplasma gondii. It is one of the most common zoonotic diseases in the world. Infection can occur by ingestion of sporulated oocysts following the handling of contaminated soil or cat litter, consumption of contaminated water or food sources, transplacental, organ transplantation or ingestion of tissue cysts in undercooked meat.
T. gondii has a strong tropism for the brain tissue, where it forms intracellular cysts within the neurons and glial cells, establishing chronic infection. The parasite is sensed by innate immune receptors (TLR) which leads to production of the cytokine IL-12, which in turn stimulates NK cells and T cells to produce IFN-γ which is the major defense mediator against T. gondii and promotes inducible nitric oxide synthase and reactive oxygen species to kill the parasite. Absence of any one of pro-inflammatory mediators (IL-12, IFN—γ and TNF-α) results in increased mortality during infection as a result of uncontrolled tachyzoite growth.
The most common form of the infections in humans are asymptomatic. But in immunocompromised patients, it may cause severe disease mainly through reactivation of cerebral toxoplasmosis which have severe neurological outcomes that lead to death.
Combination of pyrimethamine and sulfadiazine is the mainstay of chronic toxoplasmosis treatment, but their efficacy is limited due to significant toxicity, multiple adverse effects or development of drug resistance. The available therapies affect only tachyzoites in acute infection but can’t affect tissue cystic stage in chronic infection; however, Spiramycin when co-administered with Metronidazole showed significant reduction of Toxoplasma brain cyst count.
Mesenchymal stem cells are self-renewing cells that can repair or restore several tissues, including the CNS. Stem cells can cross the blood brain barrier and reverse neuronal damage. MSCs treatment modulates the immune response and reduces the expression of pro-inflammatory cytokines, biasing the immune response from a predominantly pro-inflammatory profile to a predominantly anti-inflammatory profile. MSCs secret certain cytokines that are helpful for anti-apoptosis and antifibrosis, including vascular endothelial growth factor, insulin-like growth factor, and hepatocyte growth factor. Recently, stem cell therapy was evaluated in treatment parasitic infections as they was found to relieve S. japonicum-induced liver injury, fibrosis and prolong the survival of infected mice.There is a trial to use MSCs in Leishmania major infection and cerebral malaria.
The current work was done to evaluate the potential therapeutic effect of BM-MSCs on chronic cerebral toxoplasmosis in experimentally infected mice.
BM-MSCs were obtained from tibiae and femurs of 7-wk-old Albino donor rats. Nucleated cells were cultured in the complete culture medium, incubated in 5% humidified CO2 and examined daily by inverted microscope. When cultures become confluent, cells were detached from the flasks trypsin/EDTA. Viability of cells was determined by Trypan blue, then cells were counted by a hemocytometer and adjusted to 106 cell/ml.
Female Swiss albino mice (n=100) were divided into five groups with 20 mice in each group:
• group I (infected-MSCs treated) (n=20): chronically infected mice, intravenously injected with a single dose of 5 x 105 allogenic MSCs/0.5ml/mouse, 2 months post infection.
• group II (infected-MSCs and drug treated) (n=20): chronically infected mice, treated with both; allogenic MSCs and Spiramycin (400 mg/kg)- Metronidazole (500 mg/kg), orally using nasogastric feeding tube, daily for 7 days, 2 months post infection.
• group III (infected-drug treated) (n=20): chronically infected mice, treated with 400 mg/kg of Spiramycin and 500 mg/kg of Metronidazole, orally using nasogastric feeding tube, daily for 7 days, 2 months post infection.
• group IV (infection control group) (n=20): chronically infected mice with brain cysts of the Me49 strain of T. gondii, at a dose of 20 cysts/0.2ml/mouse orally, using nasogastric feeding tube.
• group V (MSCs-control group) (n=20): Non- infected mice, intravenously injected with a single dose of 5 x 105 allogenic MSCs/0.5ml/mouse.
Mice (n=5) from each group were euthanized by cervical dislocation, at the 7th, 14th days after starting treatment administration. Deaths of mice (10 mice in each group) were recorded daily for 7 months, 2 months post infection.
Results were assessed by brain cyst count in Giemsa stained brain homogenate, histopathological examination of brain sections and survival rate.
a) As regards the mean Toxoplasma brain cyst count:
• After 7 and 14 days, group I (MSCs treated) was significantly lower than group II, significantly higher than group III and non-statistically different from group IV.
• group II (MSCs and Drug treated) was significantly higher than group III and group IV
• group III (Spiramycin-Metronidazole treated) showed significant decrease in brain cyst count versus group IV.
b) As regards histopathological examination of brain sections:
• group I (MSCs treated) showed the least histopathological inflammatory changes which was significantly lower than that of group IV.
• group II (MSCs and drug treated) revealed the most profound histopathological inflammatory changes which was significantly higher than that of group IV.
• group III (Spiramycin-Metronidazole treated) showed mild to moderate inflammatory changes with non-statistically significant difference from group IV.
• group V (non-infected injected with MSCs) showed normal cerebral architecture.
c) As regards survival rate:
Results of the cumulative survival of mice showed that, 50% and 100% of group I and group V respectively, survived during the whole experimental period.
• Among the infected groups, group I showed the highest mean survival time which was statistically significant versus group IV.
• group II showed the lowest mean survival time, which was statistically significant versus group IV.
• Mean survival time in group III showed non-significant difference versus group IV.
from the above results, MSCs have an anti-inflammatory effect and prolong the survival of the infected mice by their anti-inflammatory and anti-apoptotic effect, but could not eliminate the parasite as they didn’t affect the brain cyst count.
Combination of MSCs and Spiramycin-Metronidazole might deteriorate the infection process as this combination caused increase in the brain cyst count, sever inflammation and high mortality. This may be due to synergistic immunosuppressive effect, as both MSCs and Spiramycin caused increased level of IL-10 which decreased levels of IFN-γ and IL-12 leading to reactivation and fulminant Toxoplasma encephalitis.