Chemokine-directed leukocyte migration is a critical component of all innate and adaptive immune responses. The atypical chemokine receptor ACKR2 is expressed by lymphatic endothelial cells and scavenges pro-inflammatory CC chemokines to indirectly subdue leukocyte migration. This contributes to the resolution of acute inflammatory responses in vivo. ACKR2 is also universally expressed by innate-like B cells, suppressing their responsiveness to the non-ACKR2 ligand CXCL13, and controlling their distribution in vivo. The role of ACKR2 in autoimmunity remains relatively unexplored, although Ackr2 deficiency reportedly lessens the clinical symptoms of experimental autoimmune encephalomyelitis induced by immunization with encephalogenic peptide (MOG35–55). This was attributed to poor T-cell priming stemming from the defective departure of dendritic cells from the site of immunization. However, we report here that Ackr2-deficient mice, on two separate genetic backgrounds, are not less susceptible to autoimmunity induced by immunization, and in some cases develop enhanced clinical symptoms. Moreover, ACKR2 deficiency does not suppress T-cell priming in response to encephalogenic peptide (MOG35–55), and responses to protein antigen (collagen or MOG1–125) are characterized by elevated interleukin-17 production. Interestingly, after immunization with protein, but not peptide, antigen, Ackr2 deficiency was also associated with an increase in lymph node B cells expressing granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine that enhances T helper type 17 (Th17) cell development and survival. Thus, Ackr2 deficiency does not suppress autoreactive T-cell priming and autoimmune pathology, but can enhance T-cell polarization toward Th17 cells and increase the abundance of GM-CSF+ B cells in lymph nodes draining the site of immunization.

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Objectives: Small colony variants (SCVs) of Pseudomonas aeruginosa are often isolated in CF that shows a number of changes favouring chronic colonisation. In a murine model of chronic pulmonary colonisation with P. aeruginosa, a phenotypically stable SCV arose during the course of infection. We characterised the genomic and transcriptomic characteristics of the SCV compared to the parent strain, to establish the mechanism behind the switch to the SCV phenotype. Methods: The SCV arose within three days of colonisation. Genomic and transcriptomic analysis was performed by Illumina sequencing. Results: The SCV showed a highly stable phenotype on repeated subculture. Analysis showed typical SCV colony morphology with markedly increased biofilm production. Pulsed field gel electrophoresis showed no difference between parent NH strain and the SCV. DNA sequencing revealed few consistent changes between the parent and SCV other than a single nucleotide mutation within the algD gene. Initial RNA-seq transcriptomic analysis suggests differential expression of over 400 genes, almost all upregulated in the SCV, and many involved in adaptations to adverse environments. These included homologues of the Psl locus involved in biofilm formation, a hyperosmolar-induced protein, and EF-Tu, a bacterial ligand for the platelet activating receptor, important in epithelial adhesion. Conclusion: The heritable change in the SCV responsible for its phenotype remains obscure but may involve epigenetic change which we are investigating with PacBio TM sequencing. The observed upregulated genes give insight into the adaptations required for bacterial survival within the CF lung that could be novel therapeutic targets.