Leptin is a pleiotropic
hormone with multiple direct and regulatory immune functions.
Leptin deficiency or resistance hinders the immunologic, metabolic, and neuroendocrinologic processes necessary to thwart
infections and their associated complications, and to possibly protect against
infectious diseases following vaccination. Circulating
leptin levels are proportional to body fat mass. High circulating
leptin concentrations, as observed in
obesity, are indicative of the development of
leptin transport saturation/signaling desensitization.
Leptin bridges nutritional status and immunity. Although its role in
vaccine response is currently unknown, over-nutrition has been shown to suppress
vaccine-induced immune responses. For instance,
obesity (BMI ≥30 kg/m(2)) is associated with lower
antigen-specific antibody titers following
influenza,
hepatitis B, and
tetanus vaccinations. This suggests that
obesity, and possibly saturable
leptin levels, are contributing factors to poor vaccine immunogenicity. While
leptin-based
therapies have not been investigated as
vaccine adjuvants thus far,
leptin's role in immunity suggests that application of these
therapies is promising and worth investigation to enhance
vaccine response in people with
leptin signaling impairments. This review will examine the possibility of using
leptin as a
vaccine adjuvant by: briefly reviewing the distribution and signal transduction of
leptin and its receptors; discussing the physiology of
leptin with emphasis on its immune functions; reviewing the causes of attenuation of
leptin signaling; and finally, providing plausible inferences for the innovative use of
leptin-based
pharmacotherapies as
vaccine adjuvants.