Miglė Stančiauskaitė, Mantvydas Usvaltas, Kristina Mašalaitė, Asta Lučiūnaitė, Ieva Plikusiene
Nanobodies (Nbs) are new and promising tools for a variety of applications, including their use in medicine, although their functional activity and encounter with immune cells are still not well characterized. Our goal was to study the properties of Nbs coupled with the human IgG1 antibody Fc fragment (Nb-Fc), including their interaction with antigens, Fc receptors (FcRs), and professional phagocytes: macrophages. In our research, we employed a combination of two surface-sensitive methods: spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D). It enabled the quantitative investigation of interaction kinetics between human FcγRI (CD64) and immune complexes (IC) formed by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein Wuhan variant (SCoV2-S) and specific Nb-Fc, as well as the optical and mechanical properties of the formed layers. Human THP-1 macrophage cell culture was used to analyze antigen and IC induced inflammatory response, antigen presentation-related processes, as well as chemokine CCL2/CCR2 and CCL5/CCR5 axes. Our investigated Nb-Fcs had a high affinity for SCoV2-S that was comparable to that of the natural human antibody CR3022. ICs formed by Nb-Fcs also interacted with FcRs in a similar way to CR3022. One of the investigated Nb-Fcs distinguished itself by its very high affinity and formed relatively the largest ICs. Interestingly, only ICs formed by the other Nb-Fcs influenced cellular response. We found increased cell surface expression of CD83. This molecule plays a regulatory role in antigen presentation and is involved in the resolution of inflammation following infection. In addition, we did not find any increase in other investigated markers in THP-1 macrophages, including the inflammatory response. Overall, our data demonstrate that Nb-Fcs can be applied in a similar manner to conventional human antibodies, considering their properties.