Flaviviruses comprise a number of important human pathogens such as tick-borne encephalitis (TBE), West Nile, yellow fever, Zika and dengue viruses. They are small enveloped, arthropod-borne viruses and can infect a wide variety of cells from vertebrate and invertebrate host species. The major envelope protein E is crucial for the mechanisms of cell entry. It mediates binding to the cell surface as well as low-pH-induced fusion of the viral and endosomal membrane after uptake by receptor-mediated endocytosis. Several cellular attachment factors have been identified, but their specific role in virus entry is still obscure in many instances. Flaviviruses can also infect Fc receptor-positive cells through the internalization of infectious virus-antibody complexes, thereby bypassing the requirement for a “true” virus-specific receptor. Recent evidence has suggested that the E homodimers on the virus surface are in dynamic motion (“virus breathing”), leading to the transient exposure of sites that would be cryptic in a rigid particle, but can potentially interact with cellular ligands due to the breathing of the viral envelope. In this PhD thesis, we investigated the role of the dynamic surface of TBE virus (TBEV) in virus-cell binding and its impact on infectivity. Specifically, we addressed this question by analyzing the possible effect of E-specific monoclonal antibodies (mabs) on particle dynamics that would affect the oligomeric structure of E, virus entry as well as infection of primary and permanent cell lines. Pre-incubation of TBEV with a mab (mab A5), recognizing an epitope at the E dimer interface, enhanced binding to cells, which also resulted in increased infectivity. As revealed by biochemical analyses, mab A5 dissociated the E dimer and led to the exposure of the fusion loop (FL), which is normally buried in the dimeric E protein structure at neutral pH and becomes exposed only at the low pH in endosomes to initiate membrane fusion. We could demonstrate that the mab-induced FL exposure was responsible for enhanced binding to the plasma membrane, without leading to membrane fusion. Therefore, we conclude that the observed enhancement of infectivity was caused by an increase in particle uptake. In summary, we have identified a novel mechanism of antibody-induced enhancement of infection of flaviviruses, which is independent of Fc receptors, but is mediated by the exposure of the otherwise cryptic FL and its insertion into the host membrane already at the stage of viral attachment. Flavivirus-antibody interactions with similar effects can also occur in the context of polyclonal antibody responses and therefore have the potential to modulate the course of infection, especially when pre-existing antibodies are present in sequential infections with different flaviviruses.