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Using flow cytometry and molecular imaging, we observed that numerous lymphocytes are present within the stroma of adipose tissue.
Analysis of T cell subsets revealed that the adipose of obese subjects contained fewer CD4-positive T cells and regulatory T cells, but more CD8-positive T cells, than adipose from non-obese subjects (Nishimura 2009 Nat Med).
Around the obese adipose tissues, various cells involved in mediating immunity, such as macrophages and T cells, appear to interact with each other, and these interactions likely lead to the pathology of metabolic syndrome. In addition, the finding that CD8 gene expression is high in subcutaneous adipose tissue of obese patients, as well as mice, suggests CD8-positive T cells play an important role as a trigger of metabolic syndrome.
We clarified the negative regulation of inflammation by regulatory B cells present within adipose tissue. Flow cytometric analysis showed that 7-10% of stromal cells in visceral fat and about 30% of stromal cells in subcutaneous fat are mature B cells that strongly express IL-10. Chimeric mice with IL-10-deficient B cells show exacerbation of adipose tissue inflammation, accumulation of M1 macrophages, activation of CD8-positive T cells, and worsening of insulin resistance.
In obese mice, the function and number of regulatory B cells were diminished. These results suggest that the regulatory B cells present in adipose tissue negatively regulate adipose tissue inflammation.