Figure 2. Isogenic C57BL/6 female mice exhibit a wide range of baseline immunoreactivity (BIR) before pregnancy.

(A) 8 week-old virgin females were injected with low dose (~4 mg/ml) poly(I:C) and assessed for serum IL-6 by tail bleed 2.5hr post-injection, injected intraperitoneally (IP) with 4.0-4.4 mg/ml of high molecular weight (HMW) poly(I:C) dsRNA The BIR of ~80 virgin female CR mice is surprisingly variable, ranging from 0-12,000pg/ml when measured at 2.5h post- injection. (B) These mice can be divided into 3 groups of low, medium, and high responders. The frequency distribution of dams’ BIR defined by their serum IL-6 response to a low test dose was used to define low, medium, and high responders by quartile. (C) Testing for BIR using a low dose of poly(I:C) prior to breeding does not change the maternal response to poly(I:C) at GD12.5. Dams were tail-bled at multiple time points following poly(I:C) or saline injection at GD 12.5 and isolated serum was analyzed by Luminex for IL-6. Maternal IL-6 peaked between 2 and 2.5hr post-injection for all dams. The time-course of maternal IL-6 in unprimed mice (green squares) is the same as in primed mice tested for BIR (triangles) and both are much greater than the responses in saline-injected mice (blue open squares). Data points for each condition are shifted slightly at each time-point for better visualization. Saline injection at GD 12.5 did not alter maternal serum IL-6 at any time-point measured (n > 6). (D) BIR to low dose poly(I:C) is a stable trait in virgin female mice. One week after the first low dose injection to determine BIR, the same females were injected again with the same low dose of poly(I:C) and assessed for serum IL-6. All animals remained within their initial ‘low’, ‘medium,’ and ‘high’ BIR designation from the first to the second injection of low dose poly(I:C).