The myeloid receptor PILRβ mediates the balance of inflammatory responses through regulation of IL-27 production

Abstract

Paired immunoglobulin-like receptors beta, PILRβ, and alpha, PILRα, are related to the Siglec family of receptors and are expressed primarily on cells of the myeloid lineage. PILRβ is a DAP12 binding partner expressed on both human and mouse myeloid cells. The potential ligand, CD99, is found on many cell types, such as epithelial cells where it plays a role in migration of immune cells to sites of inflammation. Pilrb deficient mice were challenged with the parasite Toxoplasma gondii in two different models of infection induced inflammation; one involving the establishment of chronic encephalitis and a second mimicking inflammatory bowel disease in order to understand the potential role of this receptor in persistent inflammatory responses. It was found that in the absence of activating signals from PILRβ, antigen-presenting cells (APCs) produced increased amounts of IL-27, p28 and promoted IL-10 production in effector T cells. The sustained production of IL-27 led ultimately to enhanced survival after challenge due to dampened immune pathology in the gut. Similar protection was also observed in the CNS during chronic T. gondii infection after i.p. challenge again providing evidence that PILRβ is important for regulating aberrant inflammatory responses.

Figure 1. Characterization of the local inflammatory response during chronic i.p. infection.

WT and Pilrb −/− mice were challenged i.p. with 20 cysts T.gondii and followed over time. Survival of WT and Pilrb−/− mice through 100 days post infection (a). H&E of brain sections reveal larger inflammatory foci in WT mice compared to Pilrb−/−, shown at 10× magnification (b). Total number of cysts present in the CNS of mice 60–90 days post infection (c). Actual numbers of BMNCs isolated from the CNS of mice (d). Recall assays using BMNCs isolated from WT and Pilrb−/− mice and cultured for 72 hrs in the presence of Media alone, STAg, or αCD3. Levels of protein are shown as detected by ELISA for TNFα (e), IFNγ (f), NO (g), and IL-10 (h). For panel a, n = 5–15 mice/group for each of 3 experiments performed. For panel c, pooled data from 2 experiments are shown, p<0.004. For panel d, one representative experiment of 2 is shown, p<0.05. For panels e,f, and h, pooled data from 2–3 experiments are shown, *p<0.005; **p<0.002.

Figure 2. Systemic cytokine response in WT and Pilrb −/− mice after acute and chronic i.p infection.

WT and Pilrb −/− mice were challenged i.p. with either PBS or T.gondii and serum cytokine protein levels were determined by ELISA during acute infection; IL-12p70 (a), IFNγ (b), IL-10 (c), and IL-27p28 (d) all on day 5. Alternatively, IL-27p28 was analyzed on day 60–90 after challenge (e). Pooled data from 2–3 experiments is shown for all graphs. For panel b, p<0.043; for panel d, p = 0.0007 and for panel e, p<0.01.

Figure 3. Normal systemic response to infection, but enhanced resistance to high dose per oral infection.

Expression of Pilrb (a) and Pilra(b) mRNA in the ileum of infected WT and Pilrb −/− mice at various timepoints after infection. Survival of WT and Pilrb−/− mice after high dose oral infection, n = 8–11 mice/group for each of 3 experiments performed (c). H&E of ileum sections from WT (top panels) and Pilrb−/− (lower panels), at day 0 (5×) or day 10 post-peroral challenge 5× and 20× magnification, respectively. Arrows indicate the presence of blood (d). Levels of cytokine protein present in the serum of naïve or infected mice at various timepoints, IL-12p70 (e) and IFNγ (f).

Figure 4. Host survival is characterized by increased capacity to produce IL-27p28.

Recall assays using MLNs at day 5 (a); and splenocytes at day 7 (b and c, left panels) or day 10 (b and c, right panels) after peroral challenge. Amount of IFNγ (a, top graph; and b, left and right) or IL-10 (a, bottom graph; and c, left and right) detectable in supernatants of WT (grey bars) and Pilrb−/− (black bars) after 3 days of culture in media alone, with STAg, or with αCD3. For panel a, one representative experiment of two shown; for panels b and c, combined data from 3 independent experiments shown. Time course of IL-27p28 protein in serum from infected WT (grey bars) and Pilrb −/− (black bars) mice as detected by ELISA, mean ± SD is shown (d). Values between strains on days 5, p = 0.0219 and 7, p = 0.0318 are all significantly different. Recall assay using MLNs at day 5 post-peroral infection and cultured as above. Amount of IL-27p28 detectable in supernatants after 3 days of culture (e). Mean ± SD are shown. For STAg, p = 0.0143; for αCD3, p = 0.0371.

Figure 5. Cytokine mRNA expression in dendritic cells and macrophages from infected mice.

Populations of DCs and macrophages were enriched from the spleens of WT and Pilrb −/− mice 5 days after i.p. challenge. Cells were then analyzed by RT-PCR for mRNA levels of IL27p28 (a) EBi3 (b) and IL-10 (c). Pooled data from one of two representative experiments is shown.

Figure 6. IL-27 can mediate resistance to parasite induced immunopathology.

Expression of p28, EBi3, IL27 hyperkine, or GFP control were induced in vivo using minicircle DNA for systemic expression prior to high dose peroral infection with T. gondii. Survival curve of all groups 14 days post infection (a), p<0.02 for IL-27 vs. eGFP treatment groups. Serum cytokine levels for each treatment group at day 0 (white bars) and day 7 (black bars) post infection showing IL-27p28 (b), IL-10 (c), p<0.004, and IFNγ (d). For all panels means ± SD are shown. For panel a, n = 5 or 10 mice/group for each of 3 experiments performed. For panels b, c and d, n = 10 mice/group for the experiment shown, 2 total experiments performed.