Endocrine Abstracts

Aim: We propose that the circulating immune system and adipocyte size plays a role in the development of obesity related co-morbidities independent of body mass index (BMI).

Methods: Clinical data and blood samples were collected from patients with severe obesity attending a hospital weight-management clinic and lean healthy controls. Patients were classified into metabolically ‘healthy obese’ or ‘unhealthy obese’ groups, based upon standard cut-off points for blood pressure, lipid profile and fasting glucose. Peripheral lymphoid populations were assessed by flow cytometry. Adipocyte size, clinical data and liver histology from severely obese patients who have undergone bariatric surgery was examined. Liver biopsies were assessed for degree of non-alcoholic fatty liver disease.

Results: There were significantly lower levels of natural killer (NK) cells in the unhealthy obese group (8.2%) compared to the healthy obese group (12.6%, P=0.005), independent of age and BMI and these NK cells expressed significantly more inhibitory markers NKB1 (3% vs 17%, P=0.03) and CD158b (5.26% vs 16.7%, P=0.03) compared to the healthy obese group. Within the morbidly obese population, adipocyte size, and not BMI, correlated with fasting insulin and HOMA (R²=0.889), and degree of NAFLD (R²=0.696). Adipocyte size was significantly larger in the unhealthy group compared to the healthy group (P=0.005).

Conclusion: The circulating immune system of obese patients with similar BMI but different metabolic profiles is different with significantly higher levels of NK cells in the metabolically healthy, which express fewer inhibitory molecules. The higher levels of NK cells in the healthy obese patients could protect from the increased risk of malignancy and infection seen in obesity. In addition, adipocyte size is a better indicator of metabolic health than BMI in severely obese individuals and may be a key factor in the development of type 2 diabetes and NAFLD within this group.