Effect of Native and Minimally Modified Low-density Lipoprotein on the Activation of Monocyte Subsets.

BACKGROUND: In atherosclerosis, monocytes are essential and secrete pro-inflammatory cytokines in response to modified low-density lipoprotein (LDL). Human CD14++CD16-, CD14++CD16+ and CD14+CD16++ monocytes produce different cytokines. The objective of this research was to determine the number of monocyte subsets positives to cytokines in response to native (nLDL) and minimally modified LDL (mmLDL). METHODS: Human monocytes from healthy individuals were purified by negative selection and were stimulated with nLDL, mmLDL or LPS. Subsequently, human total monocytes were incubated with monoclonal antibodies specific for CD14 or both CD14 and CD16 to characterize total monocytes and monocyte subsets and with antibodies specific to anti-tumor necrosis factor (TNF)-α, anti-interleukin (IL)-6 and anti-IL-10. The number of cells positive for cytokines was determined and cells cultured with nLDL, mmLDL and LPS were compared with cells cultured only with culture medium. RESULTS: We found that nLDL does not induce in the total monocyte population or in the three monocyte subsets positives to cytokines. MmLDL induced in total monocytes positives to TNF-α and IL-6 as well as in both CD14++CD16+ and CD14+CD16++ and in CD14++CD16+ monocytes, respectively. Moreover, total monocytes and the three monocyte subsets expressed few amounts of cells positives to IL-10 in response to mmLDL. CONCLUSION: Our study demonstrated that nLDL did not induce cells positives to cytokines and that the CD14++CD16+ and CD14+CD16++ monocyte subsets could be the main sources of TNF-α and IL-6, respectively, in response to mmLDL, which promotes the development and progression of atherosclerotic plaque.

The role of TLR2, TLR4 and CD36 in macrophage activation and foam cell formation in response to oxLDL in humans.

UNLABELLED: Toll-like receptor (TLR)2, TLR4 and CD36 are central in inflammation and the development of atherosclerosis. Oxidized low-density lipoprotein (oxLDL) plays a critical role in this disease through its involvement in the formation of foam cells and the activation of leukocytes. The aim of this research was to analyze the role of TLR2, TLR4 and CD36 in foam cell differentiation and macrophage activation. METHODS: Human macrophages were incubated with monoclonal antibodies specific for TLR2, TLR4 and CD36 prior to stimulation with oxLDL. Subsequently, we analyzed foam cell formation, cytokine secretion, histocompatibility complex (MHC) class II molecules and CD86 expression and T cell proliferation. RESULTS: The stimulation of macrophages with oxLDL induced foam cell formation, cytokine secretion, HLA-DR and CD86 expression and T cell proliferation. The blockage of TLR2, TLR4 and CD36 reduced the secretion of IL-1ß, IL-6 and IL-8, the expression of HLA-DR and CD86, T cell proliferation and foam cell formation. However, the blockage of TLR2 did not affect the formation of foam cells. CONCLUSION: Our study demonstrates that TLR2, TLR4 and CD36 participate in the immune response to oxLDL by inducing an increase in pro-inflammatory cytokines, the expression HLA-DR and CD86 and the proliferation of T cells. However, TLR2 does not participate in the formation of foam cells, while TLR4 and CD36 play a relevant role in this process. These findings suggest that the activation of these receptors by oxLDL contributes to the pathogenesis of atherosclerosis.