Objective: To analyze the immunological characteristics of murine model of piperaquine sensitive (PQS) line and resistant (PQR) line of Plasmodium berghei (Pb) ANKA strain.
Methods: 64 Kunming mice were divided into three groups, 16 in each of groups A and C, 32 in group B (16 of 32 were used for observing survival days). Each mouse in groups A and B was infected with 1 x 10(7) erythrocytic stage parasites of PbPQS and PbPQR, respectively. Mice in group C were injected with the same volume of normal saline. On days 4, 8, 12 and 16 after inoculation, 4 mice from each group were sacrificed. Blood samples were collected for thin blood smear examination, and parasitemia rate calculated. Spleens were removed and spleen lymphocytes suspension prepared. Spleen lymphocytes were stimulated with ConA, and cell proliferation was measured by Cell Counting Kit-8 (CCK-8) assay. Nitrogen oxide (NO) and IFN-gamma level of spleen cell culture supernatants were detected by the Griess reagent and ELISA methods, respectively. Another 10 mice were each inoculated with 1 x 10(7) parasites of PbPQR line, and the mice were then challenged with lethal PQS line when the parasites turned into blue stained cells. The parasitemia and survival days were recorded.
Results: The average survival time of group A was (9.0 +/- 3.0) d, the parasitemia rate was over 50% at 6-12 days post- infection with severe anemia. On 16th day post-infection, no death was recorded in group B with a parasitemia rate of (2666 +/- 254) %. After ConA stimulation, the proliferation of spleen lymphocytes in groups A (0.65 +/- 0.08) and B (0.86 +/- 0.20) at 12 days after infection was significantly higher than that of group C (0.18 +/- 0.03) (P < 00.01). NO level in spleen cell culture supernatant increased with prolonged infection time. On 12th day post-infection, NO level of groups A [(48.80 +/- 3.49) micromol/L] and B [(54.80 +/- 2.17) micromol/L] was higher than that of group C [(7.80 +/- 0.71) micromol/L] (P < 0.01). IFN-gamma concentration in spleen lymphocytes culture supernatant increased with prolonged infection time. The highest IFN-gamma level of group A was (752.20 +/- 39.49) pg/ml on 12th day post-infection, while in group B it was (855.80 +/- 33.65) pg/ml on 8th day after infection, then decreased on 12th day [(620.20 +/- 27.11) pg/ml]. IFN-gamma level showed a significant difference between groups A and B (P < 0.01). In 10 days after challenge, the parasitemia rate in PQR group was up to (2.44 +/- 2.07)%, and gradually disappeared. No parasite was detected on 40th day after challenge and no mice died.
Conclusion: The proliferation of spleen cells, NO and IFN-gamma levels of spleen lymphocytes culture supernatant in PbANKA strain PQR line are significantly higher than that of PQS line. PbPQR line can induce certain protective immunoreaction.