We review some properties of a relativistic classical massless charged particle with spin interacting with an external electromagnetic field. We give in particular a proper definition of kinetic energy and total energy, the latter being conserved when the external field is stationary. We find that the particle’s velocity may differ from c as a result of the spin - electromagnetic field interaction, without jeopardizing Lorentz invariance.

In this study, we investigated the role of Giardia EVs in cellular communication and their potential as vaccine candidates. Our findings revealed that Giardia EVs activate pro-inflammatory signalling cascades, including SAPK/JNK and ERK1/ERK2, as well as the NF-kB pathway, resulting in IκB-α degradation and p65 translocation to the nucleus, in mouse macrophages. Moreover, Giardia EVs increased the expression of genes encoding pro-inflammatory molecules, such as Il1β, Il6, Il4, Ptgs2, Nos2, and Tnf. Interestingly, Giardia EVs enhanced the maturation status of human Mo-DCs and significantly increased T-cell proliferation with a Th1 profile. Immunization studies demonstrated that Giardia EVs elicited antigen-specific antibodies, with IgG subclasses indicating a balance Th1/ Th2 response. Mass spectrometry analysis identified EV proteins (22 KDa and 50 KDa) that bind to serum antibodies of immunized mice including elongation factor 1-alpha, Alpha-7.3 giardin, tubulin, and Variant Surface Proteins (VSP), known antigenic proteins in Giardia infections. Overall, our results indicated that Giardia EVs modulate innate immune cells in vitro, induce antibody-based immune response in vivo, and contain conserved immunogenic proteins. Consequently, Giardia EVs hold promise as a cell-free vaccine candidate for giardiasis.