Objectives: A major objective of our study is to optimize existing mouse models of autism (that currently use immunologically naïve pregnant dams) to more closely resemble the human situation, in which the immune systems of women have been previously stimulated either by natural infection or immunization prior to pregnancy. Thus, a more robust mouse model of autism could be developed, and reveal factors that are significant in the etiology and/or pathogenesis of this disorder that current models don't consider.
Methods: Female C57BL/6 (B6) mice were immunized i.p. with irradiated Balb/c spleen cells. One month later, these “immune” female B6 mice were mated with syngeneic B6 males. On gestational day12.5, pregnant females were injected i.p. with polyinosinic-polycytidylic acid (pI:C; 20 mg/kg) or PBS (control). Sera from pregnant dams were analyzed for the presence of multiple cytokines by Luminex assay. Phenotype (FACS analysis) and functional studies (proliferation, cytotoxicity, cytokine production) were performed on spleen cells from the offspring of pI:C-injected (vs. PBS-injected) dams.
Results: Significantly higher levels of IL-6 were present in maternal sera of pI:C-injected immune dams than in pI:C-injected immunologically naive dams. FACS analysis of activated spleen cells from offspring of pI:C-injected immune dams showed >5-fold increase in the percentages of CD4+ T Helper (TH) cells with intracellular IL-17A (TH17 cells) than spleen cells from offspring of PBS-injected immune dams. However, spleen cells from offspring of pI:C-injected naïve dams failed to show any increase in TH17 cells after similar activation. In addition, affinity-purified CD4+ T cells from offspring of pI:C-injected (vs. PBS-injected) immune dams also showed significantly greater ability to differentiate towards TH17 cells after activation and culture under TH17 polarizing conditions.
Conclusions: Immunization prior to immune activation during pregnancy caused higher production of IL-6 in maternal peripheral circulation, and promoted the development of pro-inflammatory TH17 cells in their offspring. Th17 cells have been implicated in mediating the incidence and/or progression of various inflammatory and autoimmune phenomena. Thus, the increase in TH17 cells in offspring of pI:C-injected immune dams indicate a pro-inflammatory phenotype, which may contribute to neuroinflammatory processes that have been observed in the brain and gastrointestinal tract of autistic individuals, and in experimental animal models of autism.