Microparticles Triggered by CO 2 Induce Colonic Lymphocyte Activation

Abstract

Background Elevations of CO2 on the order of 0.4%, as occur in poorly ventilated buildings and people with obstructive sleep apnea, stimulate neutrophil oxidative stress triggering generation of microparticles (MPs) that cause vascular injuries in colon and elsewhere (FRBM 106:406, 2017 and J Appl Physiol 123:297, 2017). We hypothesized that the MPs will alter colonic T-lymphocyte mitotic responses and CO2 and/or MPs may alter colonic microbiota. Methods Control mice and those exposed to air+0.4% CO2 for 4 days were euthanized, lamina propria CD4+ T cell isolated from distal colon to assess proliferative responses to protein from autologous fecal extracts, and for microbiome analyses after fecal DNA and RNA extractions. T-cell mitotic responses were assessed as (H3) thymidine incorporation and results normalized to responses from control cells incubated in RPMI buffer. Results CD4 cells from CO2 mice exhibited 1.60 + 0.07 (n=15 all groups, SE, p + 0.07 and 1.64 + 0.07 fold . Control CD4 cells did not respond to control fecal protein challenge (1.04 + 0.03) but did to CO2 fecal challenge (1.40 + 0.06, p . 001). Interventions that eliminated blood-borne neutrophil-derived MPs including injection with neutrophil-Ly6G specific F(ab)2 fragments and polyethylene glycol telomere B surfactant abrogated CO2 mouse CD4 cell mitotic responses: respectively, 1.08 + 0.01 and 1.02 + 0.03 fold (NS). A single injection with 500 mg/kg ascorbic acid also abrogated response, 1.02 + 0.01 fold. Fecal microbiota species identified by DNA profiling and metatranscriptome sequence abundance analysis demonstrated nominal differences due to CO2 exposures. Conclusion Colonic CD4+ T-cells are activated by circulating MPs and when MPs elevations are inhibited, colonic vascular integrity and T-cell changes do not occur. Response to ascobic acid suggests that oxidants on or derived from MPs may contribute to T-cell activation.