Phenotypic and Transcriptional Changes of Pulmonary Immune Responses in Dogs Following Canine Distemper Virus Infection.

Canine distemper virus (CDV), a morbillivirus within the family Paramyxoviridae, is a highly contagious infectious agent causing a multisystemic, devastating disease in a broad range of host species, characterized by severe immunosuppression, encephalitis and pneumonia. The present study aimed at investigating pulmonary immune responses of CDV-infected dogs in situ using immunohistochemistry and whole transcriptome analyses by bulk RNA sequencing. Spatiotemporal analysis of phenotypic changes revealed pulmonary immune responses primarily driven by MHC-II+, Iba-1+ and CD204+ innate immune cells during acute and subacute infection phases, which paralleled pathologic lesion development and coincided with high viral loads in CDV-infected lungs. CD20+ B cell numbers initially declined, followed by lymphoid repopulation in the advanced disease phase. Transcriptome analysis demonstrated an increased expression of transcripts related to innate immunity, antiviral defense mechanisms, type I interferon responses and regulation of cell death in the lung of CDV-infected dogs. Molecular analyses also revealed disturbed cytokine responses with a pro-inflammatory M1 macrophage polarization and impaired mucociliary defense in CDV-infected lungs. The exploratory study provides detailed data on CDV-related pulmonary immune responses, expanding the list of immunologic parameters potentially leading to viral elimination and virus-induced pulmonary immunopathology in canine distemper.

Canine Distemper Virus Alters Defense Responses in an Ex Vivo Model of Pulmonary Infection.

Canine distemper virus (CDV), belonging to the genus Morbillivirus, is a highly contagious pathogen. It is infectious in a wide range of host species, including domestic and wildlife carnivores, and causes severe systemic disease with involvement of the respiratory tract. In the present study, canine precision-cut lung slices (PCLSs) were infected with CDV (strain R252) to investigate temporospatial viral loads, cell tropism, ciliary activity, and local immune responses during early infection ex vivo. Progressive viral replication was observed during the infection period in histiocytic and, to a lesser extent, epithelial cells. CDV-infected cells were predominantly located within the bronchial subepithelial tissue. Ciliary activity was reduced in CDV-infected PCLSs, while viability remained unchanged when compared to controls. MHC-II expression was increased in the bronchial epithelium on day three postinfection. Elevated levels of anti-inflammatory cytokines (interleukin-10 and transforming growth factor-ß) were observed in CDV-infected PCLSs on day one postinfection. In conclusion, the present study demonstrates that PCLSs are permissive for CDV. The model reveals an impaired ciliary function and an anti-inflammatory cytokine response, potentially fostering viral replication in the lung during the early phase of canine distemper.

Induction of Cyclooxygenase 2 by Streptococcus pyogenes Is Mediated by Cytolysins.

Prostaglandin E2 (PGE2), an arachidonic acid metabolite regulating a broad range of physiological activities, is an important modulator of the severity of infection caused by Streptococcus pyogenes. Here, we investigated the role of streptococcal cytolysin S (SLS) and streptococcal cytolysin O (SLO) in the induction of cyclooxygenase-2 (COX-2), the rate-limiting enzyme in the synthesis of prostaglandins, in in vitro cultured macrophages and during in vivo infection. Macrophages were infected with S. pyogenes wild type or with the isogenic mutant strains deficient in SLS (ΔSLS), SLO (ΔSLO), or both (ΔSLS/ΔSLO), and the expression of COX-2 was determined at the transcriptional and the protein level. The results indicated that S. pyogenes induced expression of COX-2 and concomitant synthesis of PGE2 in macrophages mediated by the synergistic activity of both SLS and SLO, and involved calcium and the PKC/JNK signaling pathway. These results were validated using recombinant cytolysins. In a murine skin infection model, COX-2-positive cells were found more abundant at the site of S. pyogenes wild-type infection than at the site of infection with ΔSLS/ΔSLO mutant strain. These findings suggest that inhibitory targeting of SLS and SLO could ameliorate the adverse effects of high levels of prostaglandins during S. pyogenes infection.