Abstract 15: The Helix-Loop-Helix Factor Id3 Links Natural Helper Cells to Proliferation of Atheroprotective B-1a Cells
Natural immunity is emerging as important for atheroprotection. Natural IgM antibodies, such as E06, that recognize oxidative epitopes on LDL or phospholipids prevent atherosclerosis and are produced by the atheroprotective B cell subset, the B-1a B cell. IL5, an important B-1a B cell mitogen, can be produced by the innate lymphoid cell, the natural helper (NH) cell. We previously demonstrated that splenic B cells provide atheroprotection to B cell deficient mice, an effect dependent on the helix-loop-helix transcription factor, Id3. Taken together, these results raise the hypothesis that Id3 may be an important regulator of splenic B-1a B cells and natural immunity in atheroprotection.
Methods and Results Id3-/-Apoe-/- mice at 8 weeks old had fewer B-1a cells in the spleen (200672 ±58019, n = 9) compared to Id3+/+Apoe-/- mice (511840 ±88811, n = 9) as determined by flow cytometry. Consistent with fewer B-1a B cells, there were lower levels of serum E06 in Id3-/-Apoe-/- mice compared to Id3+/+Apoe-/- mice (1573 ±300 RLU vs. 2807 ±263 RLU respectively, n = 8 for each group) as assessed by ELISA. Id3-/-Apoe-/- mice had decreased B-1a B cell homeostatic proliferation compared to Id3+/+Apoe-/- mice (30.0 ±3.3% vs. 54.4 ± 1.2% respectively, n = 4) as measured by in situ CFSE. However, B-1a B cell proliferation and number and levels of E06 were unchanged in mice with B cell specific deletion of Id3 compared to controls. To determine if Id3 is required for IL33 induced levels of IL5, IL33 or vehicle control was i.p. injected into Id3+/+Apoe-/- mice or Id3-/-Apoe-/- mice every 3 days for 7 days. Id3-/-Apoe-/- mice had less IL33 induced serum IL5 levels (5.1 ±3.1 pg mL-1, n = 5) compared to Id3+/+Apoe-/- mice (67.4 ±22.9 pg mL-1, n = 4). Indeed, loss of Id3 significantly attenuated IL33 induced IL5 production in NH cells measured by flow cytometric intracellular cytokine staining (Id3-/-Apoe-/-: 31.1 ±5.4%, n = 6 vs. Id3+/+Apoe-/-: 50.3 ±4.3%, n = 6). NH cells are also present and can to produce IL5 in response to exogenous IL33 (vehicle: 4.0 ±1.4%, n = 4 vs. IL33: 14.7 ±2.4%, n = 4) in the aortic adventitia/perivascular adipose tissue of Apoe-/- mice.
Conclusion Results provide the first evidence implicating Id3 as a key regulator of NH cell IL5 production and B-1a B cell proliferation.
- © 2013 by American Heart Association, Inc.