Omicron sub-lineage BA.5 infection results in attenuated pathology in hACE2 transgenic mice

Omicron recently emerged sub-lineage BA.5, together with BA.4, caused a 5th wave of coronavirus disease (COVID-19) in South Africa and subsequently emerged as a predominant strain globally due to its high transmissibility. The lethality of BA.5 infection has not been studied in acute hACE2 transgenic (hACE2.Tg) mice models. Here, we investigated tissue-tropism and immuno-pathology induced by BA.5 infection in hACE2.Tg mice. Our data show that intranasal BA.5 infection in hACE2.Tg mice result in attenuated pulmonary infection and pathology with diminished COVID-19-induced clinical and pathological manifestations. BA.5, similar to Omicron (B.1.1.529), infection led to attenuated production of inflammatory cytokines, anti-viral response and effector T cell response as compared to the ancestral strain. Mice recovered from B.1.1.529 infection showed robust protection against BA.5 infection with reduced lung viral load and pathology. Our data provide insights as to why BA.5 infection escapes ..., Flow cytometry and intracellular cytokine staining
SCS obtained from spleen and dLN were either surface stained by using fluorescent anti-mouse antibodies in FACS buffer (PBS with 1% FBS) and analysed as previously described (Rizvi et al, 2021 & 2022); or were in-vitro in the presence of RBD (2µg/ml) or its absence (with phorbol 12-myristate13-aceate (PMA; 50 ng/ml; Sigma-Aldrich) and ionomycin (1 µg/ml; Sigma-Aldrich). RBD stimulation was performed for 6 days and was used for intracellular cytokine staining. For PMA + Ionomycin cells were activated for 4 h in the presence of Monensin (#554724 Golgi-Stop, BD Biosciences). All the cells were first washed and blocked with Fc block (anti-mouse CD16/32, Biolegend) at room temperature (RT) for 20 min. Thereafter, cells were used for  surface staining with α-CD3, α-CD4, α-CD8, α-CD11b, α-NK1.1, α-Gr1, α-c-kit, α-γδTCR, α-FcƐr1α for 20 min at RT in dark. Thereafter, cells were fixed in Cytofix and permeabilized with Perm/Wash Buffer using ..., FLowJo for FACS files.
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