Lymphocystis disease is the main viral pathology reported in gilthead seabream. Its etiological agent is Lymphocystis disease virus 3 (LCDV-Sa), genus Lymphocystivirus, family Iridoviridae. There are no effective treatments or vaccines for LCDV control, thus the main aim of this study was to develop a DNA vaccine, and to evaluate both the protection conferred against LCDV-Sa infection and the immune response in vaccinated fish. The vaccine was constructed by cloning the mcp gene (ORF LCDVSa062R) into pcDNA3.1/NT-GFP-TOPO. Two independent vaccination trials were conducted. In the first one, 5–7 g fish were intramuscularly injected with the vaccine (pcDNA-MCP) or the empty-plasmid, and the distribution and expression of the vaccine was investigated. Furthermore, vaccinated fish were challenged with LCDV-Sa in order to access the protective capacity of the vaccine. In the second trial, 70–100 g fish were vaccinated as specified, and the immune response was evaluated analyzing the expression of 23 immune-related genes and the production of specific antibodies. The results showed that the vaccine triggers an immune response characterized by the overexpression of genes relating to the inflammatory process, but not the innate antiviral immunity relating to type I IFN (interferon), and also induces the production of specific neutralizing antibodies, which could explain the protection against LCDV-Sa in vaccinated fish.

SUMMARY: The mechanisms by which viruses enter host cells are crucial for their ability to infect and cause disease, serving as major targets for both host immune responses and therapeutic strategies. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry process is primarily driven by the binding of the viral spike (S) protein to the angiotensin-converting enzyme 2 (ACE2) receptor, in conjunction with the activity of endosomal cathepsin L and the serine protease transmembrane protease serine 2 (TMPRSS2). Nevertheless, recent scientific advances have expanded our understanding of SARS-CoV-2 entry mechanisms, uncovering alternative receptors and novel cofactors that may enhance viral tropism and adaptability. Given the critical role of the SARS-CoV-2 S protein in mediating host cell entry, it has become a primary target for prevention and therapeutic strategies. However, the continuous spread of SARS-CoV-2 has led to the emergence of S protein variants that may potentially confer a fitness advantage or modify key aspects of SARS-CoV-2 biology, such as transmissibility, infectivity, antigenicity, and/or pathogenicity, posing significant challenges to the efficacy of current interventions. In this review, we provide an updated and comprehensive overview of the latest advances in SARS-CoV-2 entry pathways and molecular mechanisms, exploring their implications for antiviral drug discovery, vaccine design, and the development of other biomedical strategies while addressing the challenges posed by the ongoing evolution of the virus.

Swine are a crucial species in influenza A virus (IAV) ecology, capable of supporting replication and consequently evolution of human, avian, and swine strains. They are also the source of the 2009 pandemic H1N1 virus (H1N1pdm09). Understanding how swine IAV breach the species barrier is essential for detection of potentially pandemic viruses, but is often overlooked compared to avian IAV. We hypothesize that the HA–NA balance of (pre)pandemic swine viruses is a key feature that needs adjustment as swine and humans differ in their sialoglycome. We focused on a set of (pre)pandemic swine viruses collected in Mexico following the H1N1pdm09 emergence. Phylogenetic analysis showed that the emergence was preceded by substitutions in HA and NA predicted to affect their function. Thus, HA acquired substitution A227E, previously shown to reduce receptor binding in H1N1pdm09, while NA obtained substitution S369N in the 2nd sialic acid binding site (2SBS) predicted to reduce NA cleavage. The substitutions’ effect on the HA–NA balance, was confirmed with biolayer interferometry using recombinant proteins attached to nanoparticles. Engineering recombinant attenuated influenza viruses with swine HA and NA with/without the mentioned substitutions, showed that the 2SBS substitution negatively affected replication in primary human and swine cultures. Interestingly, replication was restored by the HA substitution. Overall, we show that the emergence of H1N1pdm09 in humans was preceded by substitutions in HA and NA that were acquired in swine and adjusted the HA–NA balance. We hypothesize that adjustment of the HA–NA balance was a critical step for crossing the host–species barrier.