['Atherosclerosis is an immunoinflammatory disease. Here we examined the role of leukocyte-derived interleukin 10 (IL-10) on advanced atherosclerosis development in low-density lipoprotein receptor knockout (LDLr-/-) mice.', 'Bone marrow cells harvested from C57BL/6 IL-10-/- and IL-10+/+ mice were transplanted into irradiated male LDLr-/- mice. Four weeks after transplantation, mice were fed a high-fat cholate-free diet for 14 weeks. Despite no differences in weights, serum total, and HDL-cholesterol levels between the 2 groups, IL-10 deficiency in leukocytes induced a >2-fold increase in lesion development in the thoracic aorta compared with controls. We also found a significant 35% increase in aortic root lesion area of IL-10-/- mice compared with IL-10+/+ mice. Furthermore, IL-10 deficiency led to a marked increase in lymphocyte and macrophage accumulation associated with a significant reduction in collagen accumulation. Finally, transfer of IL-10-/- splenocytes to LDLr-/- mice resulted in a 3-fold increase in lesion size in the aortic sinus compared with mice transplanted with IL-10+/+ splenocytes.'] Is leukocyte-derived interleukin 10 required for protection against atherosclerosis in low-density lipoprotein receptor knockout mice?