Figure 4.

Bats are the natural reservoir of betacoronaviruses: immune specificities.

Bats are increasingly recognized as the natural reservoirs of viruses of public health concern.The SARS-CoV-2 that emerged from Wuhan shared 96% identity with a bat-borne coronavirus at the whole-genome level.⁵³ Bats primary immune cells exhibit dampened activation of the NLRP3 inflammasome compared to human or mouse counterparts, related to a novel splice variant and an altered leucine-rich repeat domain of bat NLRP3.⁵⁴ Lower secretion of interleukin-1β in response to both ‘sterile’ stimuli and infection with multiple zoonotic viruses was observed with no impact on the overall viral loads. The study of the immune organs from wild-caught bats revealed a predominance of CD8⁺ T cells in the spleen, reflecting either the presence of viruses in this organ or the steady state. The majority of T cells in circulation, lymph nodes and bone marrow (BM) were CD4⁺ subsets. 40% of spleen T cells expressed constitutively IL-17, IL-22 and TGF-β mRNA. Furthermore, the unexpected high number of T cells in bats BM could suggest a role for this primary lymphoid organ in T celldevelopment.⁵⁵