Zika Virus Infection in Dexamethasone-immunosuppressed Mice Demonstrating Disseminated Infection with Multi-organ Involvement Including Orchitis Effectively Treated by Recombinant Type I Interferons

Chan, Jasper Fuk-Woo; Zhang, Anna Jinxia; Chan, Chris Chung-Sing; Yip, Cyril Chik-Yan; Mak, Winger Wing-Nga; Zhu, Houshun; Poon, Vincent Kwok-Man; Tee, Kah-Meng; Zhu, Zheng; Cai, Jian-Piao; Tsang, Jessica Oi-Ling; Chik, Kenn Ka-Heng; Yin, Feifei; Chan, Kwok-Hung; Kok, Kin-Hang; Jin, Dong-Yan; Au-Yeung, Rex Kwok-Him; Yuen, Kwok-Yung

At euthanasia (12-14 dpi), H&E staining of the necropsied tissues of these mice showed prominent acute inflammatory reactions with predominantly lymphocytic infiltrates. The most prominent inflammatory changes were seen in the brain (cortical parenchymal and perivascular lymphocytic infiltrates) (Fig. 4A to C), kidney (acute tubulitis and interstitial inflammation) (Fig. 4D to F), and testis (necrotic and hemorrhagic seminiferous tubules with marked lymphocytic infiltration in the perimeter of the tubules and the interstitium) (Fig. 5A to D) . ZIKV-NS1 protein expression was still visible, but to a lesser degree, in the immunohistochemical staining of the testis/epididymis, ovary/uterus, kidney, spleen, small intestine, pancreas, and salivary gland of the dexamethasone-immunosuppressed mice with ZIKV inoculation at 12-14 dpi compared with 5 dpi. In contrast, no inflammatory reaction and viral protein expression were seen in any organ of the control mice with ZIKV inoculation alone (groups 3 and 4) or dexamethasone immunosuppression alone (groups 5 and 6) ( Fig. 5C and D) . These findings confirmed that mice with ZIKV inoculation but no dexamethasone immunosuppression were not susceptible to infection as previously reported, and that the histological changes in the model mice (groups 1 and 2) were unrelated to dexamethasone-induced effects such as drug-induced testicular toxicity (Lazear et al., 2016; Dowall et al., 2016; Aliota et al., 2016; Rossi et al., 2016; Khorsandi et al., 2013) . The absence of inflammatory infiltrates in ZIKV-inoculated, dexamethasone-immunosuppressed mice without dexamethasone withdrawal (group 9) supported the role of the host immune response in eliciting the clinical and histological changes in the ZIKV-inoculated mice with dexamethasone withdrawal (groups 1 and 2). To further confirm the presence of inflammatory infiltrates and characterize the cell types involved in the host immune response, we stained the necropsied testis of the dexamethasone-immunosuppressed mice with ZIKV inoculation and those of the dexamethasoneimmunosuppressed mock-infected control mice with CD45 (pan-leukocyte) and CD8 (cytotoxic T lymphocyte) antibodies. Corroborative to the histological findings, only the testis of the dexamethasone-immunosuppressed mice with ZIKV inoculation, but not those of the control mice, stained positive for CD45 ( Fig. 5E and F) and CD8 antibodies ( Fig. 5G and H). These findings confirmed the presence of inflammatory infiltrates and especially CD8+ T lymphocytes in the testis of the ZIKV-infected mice.