AcSDKP is down-regulated in anaemia induced by Trypanosoma brucei infection in mice

Abstract

Background: Anaemia commonly results from destruction of erythrocytes in the peripheral blood and failure of the bone marrow haematopoietic cells to replenish the erythrocytes. The mechanisms involved in trypanosoma-induced anaemia, including the role of the bone marrow haematopoietic cells are incompletely understood. We studied the responses of a tetrapeptide, AcSDKP, and IL-10, and their association with bone marrow nucleated cells in a Trypanosoma brucei brucei GVR35 experimental infection model.

Methods: Mouse infection was done intraperitoneally with 1 × 10³ trypanosomes/mL. Mice were either infected or left uninfected (N = 100). At days 0, 9, 16, 23, 30, 37, and 44 post-infection, mice were euthanised and blood was collected by cardiac puncture to examine for parasitaemia and packed cell volume (PCV) and then centrifuged for plasma, which was used for cytokine ELISA. The mice's femurs were also dissected and bone marrow was collected for femur cellularity.

Results: PCV dropped from 39.6% to 27% in infected animals by day 9 and remained low (relative to uninfected mice) for the duration of the experiment. AcSDKP levels decreased from day 0 (11.5 × 104 pg/mL) to day 16 (10 × 104), and increased by day 30 (12.6 × 104). There was a significant difference at day 16 (P = 0.023) between the infected and uninfected groups. By contrast, expression of IL-10 markedly increased between day 0 (18.6 pg/mL) and day 16 (145 pg/mL) and decreased by day 30 (42.8 pg/mL). There was also a significant difference in IL-10 expression between infected and uninfected mice at day 16 (P < 0.001). Bone marrow nucleated cells were significantly reduced during periods of low plasma AcSDKP and high plasma IL-10 concentrations (5.4 × 106 infected vs 6.2 × 106 on day 0 and 4.9 × 106 infected vs 10 × 106 uninfected on day 16).

Conclusions: These data unravel a possible negative feedback interaction between AcSDKP and IL-10 in trypanosome infection. More importantly, this study implicates an IL-10/AcSDKP cytokine network in the regulation of bone marrow nucleated cells and provides a new potential mechanism in the pathogenesis of trypanosoma-induced anaemia. Further mechanistic blocking experiments on AcSDKP and IL-10 are recommended to further clarify understanding of the interaction.

Figure 1

Mean parasitaemia in mice at different time points infected with 103 parasites/ml of T. brucei GVR 35 (black), or uninfected (green) Data (±SEM; n=5) are representative of 2 independent experiments.

Figure 2

Packed cell volume values in mice (n = 5) at different time points infected with T.b.brucei GVR 35 (black) or uninfected mice (green) On day 30 post-infection, the decline in the average PCV of the infected mice was significantly greater (p < 0.001) than in the uninfected mice.

Figure 3

Total bone marrow cellularity of mice at different time points Mean cellularity was significantly lower in infected mice than in controls Data (±SEM; n=5) are representative of 2 independent experiements. Significant differences between infected animals and uninfected (day 9) *P=0.0042

Figure 4

Plasma IL-10 levels in mice. IL-10 was quantified in T.b. brucei GVR 35 infected (black), and uninfected mice (green) Data (± SEM; n=5) are representative of 2 independent experiments. Significant difference between infected and uninfected on day 16 and 30 are indicated as *P=0007 or *P<0.00001.

Figure 5

Supernatant IL-10 levels in mice. IL-10 was quantified in T.b. brucei GVR35 infected (black), and uninfected mice (green) Data (± SEM; n=5) are representative of 2 independent experiments.

Figure 6

Plasma AcSDKP levels in mice. At different times points, plasma levels were quantified in T.b.brucei GVR35 infected (black) and uninfected mice (green) Data (± SEM; n=5) are representative of 2 independent experiments. Significant differences between infected and controls are indicated as *P=0.0230 (day 16) or *P=0.0096 (day 23). Differences that are not significant are indicated as ^•P=0.4408..