Furthermore, treatment of CD4 + T cells in vitro with IL-6 leads to much greater upregulation of p-STAT3, and IL-17A in ASD subjects than similarly treated CD4+ T cells in TDC group.
Thirty-eight studies with total of 2487 participants (1393 patients with ASD and 1094 control subjects) were included in the meta-analysis; 13 for interferon (IFN)-γ, 17 for interleukin (IL)-1β, 22 for IL-6, 19 for tumor necrosis factor (TNF)-α, 4 for IL-1α, 6 for IL-2, 4 for IL-7, 8 for IL-8, 14 for IL-12, 3 for IL-15, 12 for IL-17, 3 for IL-18, 3 for IL-2 receptor, 3 for TNF-β, and 3 for IL-23.
Furthermore, activation of IL-17A/IL-17R signaling in neutrophils of ASD subjects leads to upregulation of phospho-NFκB, IL-6 and NOX2/ROS, thus suggesting a compelling role of IL-17A in modulation of inflammation.
Following Toll-Like receptor (TLR)-4 stimulation, the ASD<sup>GI</sup> group produced increased levels of mucosa-relevant cytokines including IL-5, IL-15 and IL-17 compared to ASD<sup>NoGI</sup>.
TNF-α, IL-6 and IL-17 have been shown to be significantly up-regulated in ASD patients compared with healthy subjects (P < 0.0001, P = 0.001 and P < 0.0001 respectively).
Moreover, in vitro activation of IL-17 receptor by IL-17A in monocytes isolated from ASD individuals leads to enhanced iNOS expression via NFκB pathway.
IL-17A has been implicated from human studies and elevated IL-17A levels in the blood have been found to correlate with phenotypic severity in a subset of ASD individuals.
Of the 11 cytokines measured only concentrations of TNF-α (p=0.002), IL-1β (p=0.02) and IL-17a (p=0.049) were significantly increased in ASD children compared to typically developing controls, but only TNF-α concentrations were positively correlated with severity of ASD symptoms on all 5 different ABC sub-scales and were predictive of an ASD phenotype (area under the curve = 0.74).