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

Summary 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 (α G al C er) 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 α G al C er 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 α G al C er given on pnd 7 resulted in only marginal boosting. Consistently, immunostaining of the spleen sections from α G al C er‐treated pnd 17 immunized neonates showed a higher number of K i67 + 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 α G al C er stimulation, whereas cell proliferation was increased markedly by α G al C er after pnd 7, and became dramatic around neonatal pnd 17–18, which was accompanied by increased B , T and NK T cell populations in the spleen. In addition, in pnd 17 spleen cells, α G al C er significantly stimulated the production of NK T cytokines, interleukin ( IL) ‐4 and interferon ( IFN)‐ γ, and promoted the proliferation of CD 23 + B cells, a subset of B cells enriched in germinal centres. These data suggest that α G al C er 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.