Objectives: One objective of the present study is to determine if in utero exposure of the fetus to cytokines elicited by maternal immune stimulation (i.e., first hit), results in a developmental programming of the immune system. A second objective is to determine whether these changes persist postnatally and into adulthood, such that upon subsequent exposure to an immune stimulus (i.e., second hit), offspring exhibit an altered response.
Methods: Female C57BL/6 (B6) mice were immunized with allogeneic Balb/c spleen cells. One month later, immune and immunologically naïve wild-type (WT) B6 female mice were mated with B6 males. On gestational day 12, pregnant dams were injected i.p. with PBS (control) or poly(I:C), and scored for sickness behavior prior to and after injections. Sera and amniotic fluids from dams were tested for the presence of multiple cytokines, using a bead-based multiplex Luminex platform, and lymphocyte phenotype/functional analyses were performed on their offspring. In addition, offspring were given second immune stimulus, either by i.p. zymosan injection to induce a localized antigen non-specific acute inflammatory response or MOG35-55 to induce a systemic antigen-specific experimental autoimmune encephalomyelitis (EAE). Offspring were assessed for qualitative and quantitative differences in their responses to these immune stimuli.
Results: Overall, pregnant dams injected with poly(I:C) showed significant sickness behavior and transient increases in levels of pro-inflammatory cytokines in sera and amniotic fluids at 2hrs post injection compared to PBS-injected pregnant dams, indicating successful maternal response to poly(I:C). Poly(I:C)-induced changes in the levels of pro-inflammatory cytokines positively correlated with the sickness behavior in pregnant mice. FACS analysis of in vitro activated spleen cells from offspring of poly(I:C)-injected (compared to PBS-injected) dams showed preferential differentiation toward Th17 cell development. Offspring of poly(I:C)-injected dams also showed heightened acute inflammatory responses as shown by significantly higher numbers of total peritoneal exudate cells (predominantly neutrophils), and significant increases in levels of pro-inflammatory cytokines in sera and peritoneal cavity fluid after zymosan injection. In addition, offspring of poly(I:C)-injected dams also exhibited significantly earlier onset and higher frequency of clinical symptoms of EAE following immunization with MOG35-55.
Conclusions: These results demonstrate that offspring of poly(I:C)-injected dams possess a pro-inflammatory phenotype, thus exhibiting more robust innate and adaptive responses upon postnatal immune stimulation. Such “fetal programming” of offspring from poly(I:C)-injected dams not only persist into neonatal and adult life, but also can have profound consequences on health and disease.