B76-12 Decay Accelerating Factor (CD55) Is Necessary for Complement Activation and T Helper Cell Recruitment in Cigarette Smoke (CS)-exposed Lungs

Rationale The complement cascade, critical part of lung innate immunity, has recently been implicated in CS-induced sterile inflammation. We and others showed that chronic obstructive pulmonary disease (COPD) patients and CS-exposed mice had elevated complement lung deposition but decreased complement inhibitor, CD55. These studies also suggested a link between CD4+ Th1 cells in smokers and COPD individuals, and CD55 deficiency leading to higher IFN-gamma-producing T cells, a key driver for emphysema progression. We hypothesized that CS-mediated complement deposition in the lung drives complement receptor C3aR+ Th1 recruitment and IFN-gamma secretion in CD55-/- mice, leading to emphysema. Methods We used lung and blood samples from COPD individuals, transgenic CD55-/- and wild-type (WT) mice under short (1-month) and long-term (6-month) CS exposure, and primary murine lymphocytes. Complement activation (C3, C4) and deposition (C5b9) in the blood and lungs were assessed using ELISA and immunofluorescence. Airspace enlargement was measured in mice using Flexivent and stereologic morphometry. EL4 T lymphoblasts, and WT and CD55-/- naïve CD4+ T cells were differentiated into Th1 cells and exposed to CS extract. CD4+ T cells polarization and activation was measured by FACS, qPCR, western blot, and ELISA. Results We detected higher C4a/total C4 ratio (2.33±1.1 pg/mL) in plasma of COPD patients vs. non-smokers (0.96±0.7 pg/mL, p < 0.0001, t-test), decreased CD55 expression, and C5b9 deposition in the lung of COPD patients. Similarly, short- and long-term CS-exposed WT mice had higher C3 and C5b9 lung deposition vs. mice under air-control (AC), while CS-exposed CD55-/- mice had even higher complement deposition. At 1-month, CS-induced complement activation in CD55-/- mice led to higher Th1 cells (19.17%±7.1) in the spleen vs. AC-CD55-/- mice (16.00%±5.7). At 6-month CS-induced complement activation in CD55-/- mice was associated with higher static compliance and mean linear intercept than CS-WT, AC-CD55-/- or AC-WT mice (p < 0.05, ANOVA 1-way). Interestingly, CS-CD55-/- mice also had higher CD4+ and CD8+ T cells in the lung parenchyma (p < 0.05, ANOVA 1-way). In vitro CS treatment (2.5%, 4h) enhanced C3aR+expression and Th-1 polarization in both EL4 T lymphoblast and primary CD4+ T cells (16.53%) vs AC- treated cells (7.38%), with higher C3aR (17-fold), T-bet (4-fold), and IFN-gamma (1.5-fold) expression (p < 0.005, t-test). Conclusion CS-mediated sterile inflammation increases complement activation, Th1 lymphocytes lung recruitment, and emphysema development in CD55-/- mice, suggesting a crosstalk between lung innate (CD55) and adaptive (Th1 cells) immunity. Further studies will define the molecular pathways behind the crosstalk identifying new therapeutic targets in COPD. This abstract is funded by: NIH