Autoimmunity to low-density lipoprotein (LDL) is linked to atherosclerosis, with LDL immunization proposed as a preventive measure, but the mechanisms of atheroprotective immunity are not well understood. We investigated T-cell responses to LDL using 2 T-cell receptor transgenic mouse strains. At 52 weeks, BT1×HuBL mice showed reduced atherosclerosis, increased humoral responses against LDL, and lower plasma cholesterol. Conversely, BT3×HuBL mice had reduced atherosclerosis without changes in cholesterol, linked to increased type 1 regulatory T cells, interleukin (IL)-10 production, and decreased characteristics of plaque stability. In human plaques, IL10 mRNA negatively correlated with collagen content, and IL-10 inhibited collagen production in vitro. We conclude that atheroprotective LDL immunity elicits 2 distinct pathways: lipid-lowering immune responses and local anti-inflammatory IL-10 production. Because IL-10 is associated with decreased plaque stability and increased risk of cardiovascular events, treatments aimed at promoting IL-10 signaling over extended periods to reduce vascular inflammation should be carefully monitored.