SARS-CoV-2 infection impairs NK cell functions via activation of the LLT1-CD161 axis

Abstract

IntroductionNatural killer (NK) cells plays a pivotal role in the control of viral infections, and their function depend on the balance between their activating and inhibitory receptors. The immune dysregulation observed in COVID-19 patients was previously associated with downregulation of NK cell numbers and function, yet the mechanism of inhibition of NK cell functions and the interplay between infected cells and NK cells remain largely unknown. MethodsIn this study we show that SARS-CoV-2 infection of airway epithelial cells can directly influence NK cell phenotype and functions in the infection microenvironment. NK cells were co-cultured with SARS-CoV-2 infected epithelial cells, in a direct contact with A549ACE2/TMPRSS2 cell line or in a microenvironment of the infection in a 3D ex vivo human airway epithelium (HAE) model and NK cell surface expression of a set of most important receptors (CD16, NKG2D, NKp46, DNAM-1, NKG2C, CD161, NKG2A, TIM-3, TIGIT, and PD-1) was analyzed. ResultsWe observed a selective, in both utilized experimental models, significant downregulation the proportion of CD161 (NKR-P1A or KLRB1) expressing NK cells, and its expression level, which was followed by a significant impairment of NK cells cytotoxicity level against K562 cells. What is more, we confirmed that SARS-CoV-2 infection upregulates the expression of the ligand for CD161 receptor, lectin-like transcript 1 (LLT1, CLEC2D or OCIL), on infected epithelial cells. LLT1 protein can be also detected not only in supernatants of SARS-CoV-2 infected A549ACE2/TMPRSS2 cells and HAE basolateral medium, but also in serum of COVID-19 patients. Finally, we proved that soluble LLT1 protein treatment of NK cells significantly reduces i) the proportion of CD161+ NK cells, ii) the ability of NK cells to control SARS-CoV-2 infection in A549ACE2/TMPRSS2 cells and iii) the production of granzyme B by NK cells and their cytotoxicity capacity, yet not degranulation level. ConclusionWe propose a novel mechanism of SARS-CoV-2 inhibition of NK cell functions via activation of the LLT1-CD161 axis.

The proportion of CD161 on CD56+ NK cells in peripheral circulation associates with clinical features and disease activity of primary Sjögren's syndrome

“…These results suggested that the decrease of CD161 + CD56 + NK cells may contribute to the progression of pSS. Lenart et al found that activation of the LLT1‐CD161 axis can inhibit granzyme B and IFN‐γ production by NK cells and hamper the function of NK cells 29 . CD161 is expressed in the early stage of NK cell development, and in the peripheral circulation, the crosslinking of CD161 leads to upregulate the expression of IFN‐γ and inhibits the cytotoxicity of NK cells 10,30 .…”

“…Lenart et al found that activation of the LLT1-CD161 axis can inhibit granzyme B and IFN-γ production by NK cells and hamper the function of NK cells. 29 CD161 is expressed in the early stage of NK cell development, and in the peripheral circulation, the crosslinking of CD161 leads to upregulate the expression of IFN-γ and inhibits the cytotoxicity of NK cells. 10,30 Another study showed that CD161 on NK cells combined with its ligand on target cells and inhibited NK cytotoxicity by activating acidic sphingomyelinase.…”

Natural Killer Cells Do Not Attenuate a Mouse-Adapted SARS-CoV-2-Induced Disease in Rag2−/− Mice

“…In severe COVID patients, NK cells are exhausted due to the induced expression of the inhibitory molecules, including the overexpression of PD-1 on its surface [ 66 , 67 ]. Additionally, SARS-CoV-2 infection impairs NK cell functions by activating the LLT1-CD161 axis, leading to reduced cytotoxicity [ 68 ]. NK cells in COVID-19 patients show dysfunction, characterized by decreased quantity and impaired ability to reduce viral protein levels, similar to tumor-associated NK cells [ 69 ].…”

“…NK cells in COVID-19 patients show dysfunction, characterized by decreased quantity and impaired ability to reduce viral protein levels, similar to tumor-associated NK cells [ 69 ]. NK cells are exhausted and thereby play a negligible role in the acute phase of severe COVID-19 disease in patients [ 20 , 21 , 66 , 67 , 68 , 69 ]. Our results support those clinical findings though further investigation of the exhausted and activated status of NK cells is required.…”

The Possible Role of Pathogens and Chronic Immune Stimulation in the Development of Diffuse Large B-Cell Lymphoma

“…The virus-induced ongoing inflammation and cytokines may facilitate B-cell proliferation in these patients [ 50 ]. The infected T-cells increase TIGIT and PD-1 expression, possibly leading to a more severe form of COVID-19 [ 92 ]. This negatively impacts the immune system, making way for possible B-cell malignancies.…”