SARS-CoV-2 VARIANTS-DEPENDENT INFLAMMASOME ACTIVATION

ABSTRACT

Background: Innate immunity is the first line of defense in response to pathogens, which acts locally and also leads the stimulation of adaptive immunity through at least with IL-1beta secretion. It has been shown that SARSCoV- 2 infection triggered the NLRP-3 inflammasome activation and the IL-1beta secretion. The aim of this study was to analyze and compare the level of IL-1beta secretion that is one of the most important innate immunity cytokines, in monocyte-like cells infected with 6 different variants of the SARS-CoV-2. Method(s) Six SARS-CoV-2 variants (historical (B.1, D614G), Alpha, Beta, Gamma, Delta and Omicron BA.1) were isolated from COVID-19 hospitalized patients. Viral stocks were obtained by inoculation in Vero and Vero-TRMPSS2 cells. THP-1 monocyte-like cells were cultured with RPMI-hepes 10% FBS-0.05 mM 2-mercaptoethanol. A total of 5 x 104 of THP-1 cells was plated per well in 96-wells plate and differentiated with 10nM of PMA for 24h. Differenciated- THP-1 were first primed with LPS 1mug/ml for 2h and infected with different SARS-CoV-2 variants with a MOI 0.1. IL-1beta was measured by luminescence in the supernatant after 24 h of infection. Result(s) We analyzed and compared IL-1beta secretion between SARS-CoV-2 virus 6 sublineages after infection of monocytes like THP-1. We observed that THP-1 cells infected with SARS-CoV-2 variants presented a significantly higher IL-1beta secretion than non-infected cells. Moreover, some SARS-CoV-2 variants led to a stronger IL-1beta secretion, and particularly we observed a significantly higher level of IL-1beta cells infected with Omicron BA.1 sublineage compared to other variants. Indeed, Omicron BA.1 infected cells presented the higher IL-1beta secretion (median 385.7 pg/ml IQR[302.6-426.3]) follows by the Delta variants and the historical variants (median 303.6 [266.3-391.9] and 281.9 [207.2-410], respectively). Alpha, Beta and Gamma variants presented the lowest IL-1beta secretion (median 228.1 [192.5-276.4], 219.1 [185.1-354.2] and 211 [149.8- 228.8]). Conclusion(s) We observed the inflammasome activation for the 6 SARS-CoV-2 sublineages with a variation in level of IL-1beta secretion. Indeed, our results suggested that Omicron BA.1 was more recognized by the innate immune cells than other SARS-CoV-2, which could in part, with its upper respiratory tract tropism, possibly explain its less clinical virulence. Taking together, these results suggest that the innate immunity response and precisely, IL-1beta secretion pathways were activated in a SARS-CoV-2 variants-dependent manner.