ABSTRACT
Macrophages and T-lymphocytes are known to accumulate in the white adipose tissue (WAT) of obese mice and humans, but the factors that cause this infiltration are not yet determined. Chemokines, which attract leukocytes to inflammatory sites, are candidates for this process. Macrophage inflammatory protein-1alpha (MIP-1alpha) expression is significantly elevated in WAT of obese mice and humans and positively correlates with fasting plasma insulin, but its potential role in leukocyte recruitment to WAT is unknown. MIP-1alpha-deficient, heterozygous, and wild-type mice were fed a Western diet (WD) for 16 wk. Plasma lipids, adipose tissue mass, energy expenditure, food intake, liver triglyceride content, and inflammatory cytokine expression were not different among genotypes. Gene expression of macrophage markers F4/80 and CD68, as well as T-lymphocyte marker CD3epsilon was increased in perigonadal WAT of obese WD-fed mice but was not influenced by MIP-1alpha expression level. Immunohistochemical analysis of WAT also showed no effect of MIP-1alpha on macrophage content. Two related chemokines, MIP-1beta and RANTES, had reduced expression in obese male MIP-1alpha-deficient mice compared with wild-type controls (P < or = 0.05). In mice fed the WD for 6 wk, WAT macrophage content was unchanged; however, CD8+ T-lymphocytes accumulated to a lesser extent in the MIP-1alpha-null mice. Therefore, expression of MIP-1alpha, as well as that of MIP-1beta and RANTES, increases as a consequence of weight gain, but these chemokines may not be required for the recruitment of monocytes to WAT during diet-induced obesity in mice and may impact T-lymphocyte recruitment only at early time points after WD feeding.
