Obesity and inflammation: evidence for an elementary lesion.

In obesity, an inflammatory process of the adipose tissue has been hypothesized; however, direct evidence for a tissue lesion is still lacking. Macrophage infiltration in the adipose tissue of obese individuals seems to be proven, but other alterations of the tissue have not been demonstrated. Moreover, in humans it has not been clarified whether inflammation is an early characteristic of obesity, because no data from obese children are available. In the present study, we assessed the inflammatory involvement of the adipose tissue and identified the elementary "inflammatory" lesion in a group of obese children. The study of children gives us the chance to investigate adipose tissue during early phases of obesity. In all the obese subjects, ultramicroscopic analysis of the adipose tissue demonstrated inflammatory involvement, and the extent of the lesions seemed to depend on the SD score of body mass index. The elementary lesion is a microgranuloma, with fragments of adipocytes, that evolves to fibrosis. Macrophages (and less frequently, lymphocytes or granulocytes) were found in perivascular positions. The lesions were not found in nonobese children. Our study proved that an "inflammatory" process exists in the adipose tissue of obese children, confirming previous findings in animals and obese adults and demonstrating that it is an early alteration in humans. However, the accumulation of macrophages was just one of the components of the inflammatory lesion, which also involved adipocyte degeneration, fibrosis, and, to a lesser extent, granulocyte/lymphocyte accumulation. The finding of fragments of adipocytes in the elementary lesion suggests that, at the beginning of the process, adipocytes may degenerate and that the materials generated by this process can recruit macrophages and other leukocytes. These preliminary results suggest that additional studies should be designed to clarify the cause of adipocyte fragility in obese children.