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Morbillivirus infections have been known for a long time to be associated with an acute immunosuppression in their natural hosts. Here, we show that recombinant Morbillivirus nucleoproteins from canine distemper virus, peste-des-petits-ruminants virus, and Rinderpest virus bind B-lymphocytes from dogs, goats, and cattle, respectively, similarly to measles virus nucleoprotein in humans. The use of surface plasmon resonance imaging allowed the real time detection of differential interactions between Morbillivirus nucleoproteins and FcgammaRIIb (CD32). Moreover, those nucleoproteins which bind murine Fcgamma receptor inhibited the inflammatory immune responses in mice in a Fc receptor- dependent manner. In contrast, nucleoprotein from closely related Henipavirus genus, belonging to the Paramyxoviridae family as Morbillivirus, was devoid of capacity either to bind FcgammaRIIb or to inhibit inflammatory response. Altogether, these results suggest that nucleoprotein-FcR interaction is a common mechanism used by different Morbilliviruses to modulate the immune response.

Background Protein folding in the envelope is a crucial limiting step of protein export and secretion. In order to better understand this process in Lactococcus lactis , a lactic acid bacterium, genes encoding putative exported folding factors like Peptidyl Prolyl Isomerases (PPIases) were searched for in lactococcal genomes. Results In L. lactis , a new putative membrane PPIase of the cyclophilin subfamily, PpiA, was identified and characterized. ppiA gene was found to be constitutively expressed under normal and stress (heat shock, H 2 O 2 ) conditions. Under normal conditions, PpiA protein was synthesized and released from intact cells by an exogenously added protease, showing that it was exposed at the cell surface. No obvious phenotype could be associated to a ppiA mutant strain under several laboratory conditions including stress conditions, except a very low sensitivity to H 2 O 2 . Induction of a ppiA copy provided in trans had no effect i) on the thermosensitivity of an mutant strain deficient for the lactococcal surface protease HtrA and ii) on the secretion and stability on four exported proteins (a highly degraded hybrid protein and three heterologous secreted proteins) in an otherwise wild-type strain background. However, a recombinant soluble form of PpiA that had been produced and secreted in L. lactis and purified from a culture supernatant displayed both PPIase and chaperone activities. Conclusions Although L. lactis PpiA, a protein produced and exposed at the cell surface under normal conditions, displayed a very moderate role in vivo , it was found, as a recombinant soluble form, to be endowed with folding activities in vitro .