Immune response after gastric bypass and weight loss

The immune response of 22 morbidly obese patients was measured before and 6 months after gastric bypass. In-vivo skin testing was carried out using five recall antigens. In-vitro response assessed the ability of isolated lymphocytes to take up radioactive thymidine after culture with the same antigens. The mean (+/- SD) preoperative weight of the patients of 122 +/- 14 kg declined by 33.5 +/- 8 kg after 6 months. The number of positive skin tests increased from a mean (+/- SEM) of 1.8 +/- 0.17 to 2.1 +/- 0.17 (p = 0.2). Mean (+/- SEM) induration of the skin-test response assessed at 24 hours after antigen injection increased from 4.7 +/- 0.6 mm to 5.5 +/- 0.6 mm (p = 0.35) and at 48 hours from 5.4 +/- 0.7 mm to 6.9 +/- 0.9 mm (p = 0.05). One patient who was anergic before gastroplasty responded normally 6 months later after substantial weight loss. In-vitro response, expressed as a stimulation index (+/- SEM), increased from 4.71 +/- 0.65 to 7.95 +/- 1.56 (p = 0.06) for the average of all antigens and from 12.85 +/- 2.05 to 15.79 +/- 2.84 (p = 0.2) for the largest response. The authors conclude that the response to test antigens in vitro and in vivo is not reduced significantly 6 months after gastric bypass and profound weight loss. Patients with severe vomiting, rapid weight loss or sepsis may respond differently and require individual assessment.