Regulatory T lymphocytes/Th17 lymphocytes imbalance in autism spectrum disorders: evidence from a meta-analysis.

The studies disagreed far more than chance would explain. Heterogeneity was 96% for the CD4+ finding and 90.9% to 95.1% for the regulatory T cell and Th17 findings, so a single pooled average sits on top of very inconsistent results. Each study separated and counted cells using its own flow cytometry staining method, so the studies may not have been counting exactly the same cells. In healthy people, the different subgroups within T cells can make up anywhere from 22% to 93% of total lymphocytes, which makes comparing such variable populations difficult. The regulatory T cell and Th17 results rest on only three and four studies respectively. The authors say these two results should be taken with precaution, and that limiting the number of studies per analysis cost them power. Only peripheral blood was studied, so the work says nothing about immune changes inside the brain. Several lymphocyte types had no data at all, so the picture of immune cell balance in autism is incomplete. The authors state that no causal role can be established from these findings.

Do not read this as showing that immune changes cause autism, or that treating the immune system would help. The authors state plainly that no causal role can be established, and the cell counts come from blood, not the brain. The positive findings also rest on a handful of small studies that disagreed strongly with each other.