Increased concentration of serum IFN-γ in tc-ptp^-/- mice. Serum IFN-γ in tc-ptp^-/- (▪) and tc-ptp^+/+ mice (□) at 3 weeks after birth. Mice were injected with PBS or 4 μg LPS in 150 μL PBS and bled 5 hours after injection. Results are shown as ng of IFN-γ/mL of mouse serum. Bars represent the mean values ± SE from 4 to 8 mice. Statistical significance was determined by a 2-tailed unpaired Student t test. ^*P < .05 tc-ptp^-/- +LPS compared with tc-ptp-/^- +PBS. ^**P < .01 tc-ptp-/^- +LPS compared with tc-ptp^+/+ +LPS.