Published online May 14, 2017. doi: 10.3748/wjg.v23.i18.3240
Peer-review started: December 17, 2016
First decision: December 29, 2016
Revised: January 27, 2017
Accepted: March 15, 2017
Article in press: March 15, 2017
Published online: May 14, 2017
Processing time: 150 Days and 22.5 Hours
To identify which blood and mucosal lymphocyte populations are specifically depleted by thiopurine use in vivo.
The thiopurines azathioprine and 6-mercaptopurine have been a mainstay of inflammatory bowel disease (IBD) therapy for decades, but their mechanism of action in vivo remains obscure. Although thiopurines are lymphotoxic at high doses, and have been reported to cause T cell apoptosis in vitro, their ability to control IBD at lower doses suggests that they may selectively deplete particular lymphocyte populations. Blood cells from 19 IBD patients on a thiopurine, 19 IBD patients not on a thiopurine, and 38 matched healthy control subjects were analyzed by multiple multi-color flow cytometry panels to quantify the immune cell subsets contained therein, both as a percent of cells, and as an absolute cell count. Similar analyses were performed on colon biopsies from 17 IBD patients on a thiopurine, 17 IBD patients not on a thiopurine, and 49 healthy screening colonoscopy recipients.
Complete blood counts revealed lower lymphocyte, but not monocyte or granulocyte, counts in IBD patients who were taking thiopurines at the time of sampling. This reduction was restricted to CD3-negative lymphocytes, wherein both natural killer (NK) and B cells were significantly reduced among thiopurine recipients. Among CD19+ B cells, the transitional B cells were particularly depleted, being nearly absent in both blood and colon biopsies of thiopurine recipients. No differences were associated with thiopurine use in CD8+ T cells, mucosa-associated invariant T (MAIT) cells, invariant natural killer T (iNKT) cells, gamma/delta T cells, Th1, Th17, regulatory T cells (Tregs) or naïve CD4+ T cells. However, patients with IBD had significantly more circulating FOXP3+, Helios+ Tregs and fewer iNKT and MAIT cells than healthy controls.
Thiopurine use is associated with reduced B and NK cell, but not T cell, subpopulations in the blood of IBD patients.
Core tip: Thiopurine medications have been used to treat inflammatory bowel disease (IBD) for almost half a century. However, the effect of thiopurines on the human immune system in vitro remains unclear. The enclosed manuscript performed a thorough flow cytometric analysis of peripheral blood specimens from IBD patients with or without thiopurine therapy and found significant differences in B and NK cell populations associated with therapy. These suggest that thiopurines function to suppress inflammation in IBD not by causing T cell apoptosis, as had been suggested by in vitro data, but rather by depleting other lymphocytes.