Stimulation of one or more neurons of the sympathetic nervous system, including the splenic nerve, is provided to attenuate an immune response, including an inflammatory immune response. Devices such as pulse generators and drug pumps may be used to stimulate the sympathetic nervous system to attenuate an immune response. Systems optionally having one or more sensors and operator instructions may also be used. In specific examples, stimulation of the splenic nerve of pigs with a pulse generator is shown to be safe and effective in attenuating a lipopolysaccharide-induced immune response.