α-Galactosylceramide stimulates splenic lymphocyte proliferation in vitro and increases antibody production in vivo in late neonatal-age mice

The neonatal stage is characterized by weak responses to various infections and vaccines, thus the development of efficient formulas to improve vaccine effectiveness is of high priority. The glycolipid alpha galactosylceramide (GalCer) is known as a potent immune modulator due mainly to natural killer (NK)T cell activation. Using a mouse tetanus toxoid (TT) immunization model, we observed that neonatal mice given GalCer at the time of primary immunization on postnatal day (pnd) 17 had a significantly higher TT-specific immunoglobulin (Ig)M response as well as a memory IgG response, while GalCer given on pnd 7 resulted in only marginal boosting. Consistently, immunostaining of the spleen sections from GalCer-treated pnd 17 immunized neonates showed a higher number of Ki67(+) cells in the splenic germinal centre area, suggesting a stronger response after immunization. In-vitro kinetic studies revealed that spleen cells from newborn to pnd 7 neonates did not respond to GalCer stimulation, whereas cell proliferation was increased markedly by GalCer after pnd 7, and became dramatic around neonatal pnd 17-18, which was accompanied by increased B, T and NKT cell populations in the spleen. In addition, in pnd 17 spleen cells, GalCer significantly stimulated the production of NKT cytokines, interleukin (IL)-4 and interferon (IFN)-, and promoted the proliferation of CD23(+) B cells, a subset of B cells enriched in germinal centres. These data suggest that GalCer is an effective immune stimulus in the late neonatal stage, and thus may be useful in translational studies to test as a potential adjuvant to achieve a more efficient response to immunization.