Immune memory to Sudan virus: comparison between two separate disease outbreaks

Abstract

Recovery from ebolavirus infection in humans is associated with the development of both cell-mediated and humoral immune responses. According to recent studies, individuals that did not survive infection with ebolaviruses appear to have lacked a robust adaptive immune response and the expression of several early innate response markers. However, a comprehensive protective immune profile has yet to be described. Here, we examine cellular memory immune responses among survivors of two separate Ebolavirus outbreaks (EVDs) due to Sudan virus (SUDV) infection in Uganda-Gulu 2000-2001 and Kibaale 2012. Freshly collected blood samples were stimulated with inactivated SUDV, as well as with recombinant SUDV or Ebola virus (EBOV) GP (GP1-649). In addition, ELISA and plaque reduction neutralization assays were performed to determine anti-SUDV IgG titers and neutralization capacity. Cytokine expression was measured in whole blood cultures in response to SUDV and SUDV GP stimulation in both survivor pools, demonstrating recall responses that indicate immune memory. Cytokine responses between groups were similar but had distinct differences. Neutralizing, SUDV-specific IgG activity against irradiated SUDV and SUDV recombinant proteins were detected in both survivor cohorts. Furthermore, humoral and cell-mediated crossreactivity to EBOV and EBOV recombinant GP1-649 was observed in both cohorts. In conclusion, immune responses in both groups of survivors demonstrate persistent recognition of relevant antigens, albeit larger cohorts are required in order to reach greater statistical significance. The differing cytokine responses between Gulu and Kibaale outbreak survivors suggests that each outbreak may not yield identical memory responses and promotes the merits of studying the immune responses among outbreaks of the same virus. Finally, our demonstration of cross-reactive immune recognition suggests that there is potential for developing cross-protective vaccines for ebolaviruses.

Figure 1

Cytokine levels comparison between SUDV-Gul whole antigen (A); and GP_1–649 (B) stimulation and unstimulated whole blood from Kibaale (1-year) and Gulu (12-year) ebolavirus survivors and non-infected controls (CT). Non-infected controls of Kibaale and Gulu are presented as average results since there were no significant changes between the two groups (Data not shown). Cytokine levels were measured in the plasma supernatants of samples following whole blood stimulation and resting state. Mean ± SEM, * p < 0.05.

Figure 2

Cytokine levels following SUDV/Gul whole antigen (A) and GP_1–649 (B) stimulation of whole blood from Kibaale (1-year) and Gulu (12-year) ebolavirus survivors and non-infected controls (CT). Cytokine levels were measured in the plasma supernatants of samples following whole blood stimulation. Normalization of cytokine expression levels was performed by reducing the background (unstimulated value) of each individual stimulated (SUDV/Gul whole antigen or GP_1–649) sample. Non-infected controls of Kibaale and Gulu are presented as average results since there were no significant changes between the two groups of controls (Data not shown). Mean ± SEM, * p < 0.05.

Figure 3

Cytokine levels comparison between EBOV GP_1–649 stimulation and unstimulated whole blood from Kibaale (1-year) and Gulu (12-year) ebolavirus survivors and non-infected controls (CT). Cytokine levels were measured in the plasma supernatants of samples following whole blood stimulation. Non-infected controls of Kibaale and Gulu are presented as average results since there were no significant changes between the two groups of controls (Data not shown). Mean ± SEM, * p < 0.05.

Figure 4

Cytokine levels following EBOV GP_1–649 stimulation of whole blood from Kibaale (1-year) and Gulu (12-year) ebolavirus survivors and non-infected controls (CT). Cytokine levels were measured in the plasma supernatants of samples following whole blood stimulation. Normalization of cytokine expression levels was performed by reducing the background (unstimulated value) of each individual stimulated (EBOV GP_1–649) sample. Non-infected controls of Kibaale and Gulu are presented as average results since there were no significant changes between the two groups (Data not shown). Mean ± SEM, * p < 0.05.