Bacterial superantigens and T cell receptor beta-chain-bearing T cells in the immunopathogenesis of ulcerative colitis

Abstract

Ulcerative colitis (UC) is a chronic relapsing-remitting inflammatory bowel disease (IBD) that affects the colon and the rectum producing debilitating symptoms, which impair ability to function and quality of life. The aetiology of IBD is incompletely understood, but within the lymphocyte population, specific T cell subsets are known to be major factors in the development of intestinal immune pathology while different subsets are essential regulators, controlling IBD. Hence, IBD is thought to reflect dysregulated T cell behaviour. This study was to investigate if the normal molecular configuration of the T cell receptor (TCR) repertoire is compromised in patients with UC. The percentage of T cell-bearing beta-chain 4 (TCRBV4) was high in patients with UC, and T cells showed polyclonal expansion in the presence of bacterial superantigens (SA) such as streptococcal mitogenic exotoxin Z-2 (SMEZ-2), indicating that bacterial SA promote specific TCRBV family expansion. Further, in patients with UC, the duration of UC was significantly longer in patients with skewed TCRBV4 compared with patients without TCRBV4 skewing, suggesting that long-term exposure to bacterial SA such as SMEZ-2 might promote systemic immune disorders like the remission-relapsing cycles seen in patients with UC. In conclusion, our observations in this study support the perception that the systemic activation of T cells by enteric bacterial SA might lead to a dysregulated, but exuberant immune activity causing the remission and flare-up cycle of mucosal inflammation in patients with UC. Future studies should strengthen our findings and increase understanding on the aetiology of IBD.

Fig. 1

T cell receptor β-chain (TCRBV) gene expression profile in peripheral blood mononuclear cells (PBMC) of patients with active ulcerative colitis (UC). Total RNA was extracted from PBMC and reverse-transcribed into cDNA and the adaptor was ligated. This adaptor-ligated cDNA was then used as a template for individual polymerase chain reaction (PCR) amplifications. The primer sets were then applied to the adaptor sequence and TCRBC gene elements. The PCR products were determined by semiquantitative PCR–enzyme-linked immunosorbent assay. Twenty-one of 23 (91%) patients had strongly skewed TCR repertoire in any TCRBV subfamilies and intense skew was observed in TCRBV4.

Fig. 2

The polyclonal expansion of T cell receptor β-chain 4 (TCRBV4)-bearing T cells in peripheral blood mononuclear cells (PBMC) of patients with active ulcerative colitis (UC). (a) The percentage of TCRBV4 in PBMC specimens of patients with UC was strikingly high compared with healthy individuals (P < 0·0001). Mean ± s.d. values are presented; the P-value is by the Mann–Whitney U-test. (b) The CDR3 size spectratype profiles of the TCRBV4 gene rearrangement. The TCRBV4 gene was selected among the PBMC of 14 patients with skewed TCRBV4. Each of the 14 subjects had 7–10 peaks showing a Gaussian-like distribution.

Fig. 3

Changes in the percentage frequency of T cell receptor β-chain (TCRBV) families following stimulation by two different bacterial superantigens (SA), toxic shock syndrome toxin 1 (TSST-1) and streptococcal mitogenic exotoxin Z-2 (SMEZ-2). TSST-1 stimulated TCRBV2-bearing T cells (a) and did not stimulate TCRBV4-bearing T cells (b). SMEZ-2 stimulated TCRBV4-bearing T cells (d) without the expansion of TCRBV2-bearing T cells (c). The P-values are by paired t-test.

Fig. 4

Elevated anti-streptococcal mitogenic exotoxin Z-2 (SMEZ-2) antibody in patients with active ulcerative colitis (UC) who had skewed T cell receptor β-chain 4 (TCRBV4). (a) The anti-SMEZ-2 titre was significantly higher in patients with skewed TCRBV4 compared with healthy volunteers (P = 0·0305, by Mann–Whitney U-test). (b) The correlation of the percentage of TCRBV4 with anti-SMEZ-2 titre (n = 23, ρ= 0·606, P = 0·0045, by Spearman's rank correlation). The anti-streptolysin-O (ASO) level (c) also showed significant correlation with the anti-SMEZ-2 titre (n = 27, ρ= 0·352, P = 0·0149, by Spearman's rank correlation test), but no correlation with anti-toxic shock syndrome toxin 1 (TSST-1) titre was seen.

Fig. 5

Polyclonal expansion of T cell receptor β-chain 4 (TCRBV4) and TCRBV8-bearing T cells within the intestinal mucosa of patients with active ulcerative colitis (UC). (a) The percentage of TCRBV4, BV6·2, BV6·5 and BV8 in intestinal samples from patients with UC were significantly higher than the level in the peripheral blood mononuclear cells (PBMC) of healthy individuals (P = 0·0297, P = 0·0174, P = 0·0066 and P = 0·0209, respectively). Mean ± s.d. values are presented; the P-values are by Mann–Whitney U-test. (b), CDR3 size spectratype profiles of TCRBV gene rearrangements. Three patients who had skewed TCRBV4 within the intestinal mucosa were selected for spectratyping. On the TCRBV4 and TCRBV8 genes, these three subjects had 6–8 peaks with Gaussian-like distribution and spectratype profile except on TCRBV8 in UC104, showing polyclonal expansion.

Fig. 6

Significant (P = 0·0314, by Mann–Whitney U-test) association between duration of ulcerative colitis and T cell receptor β-chain 4 (TCRBV4) skewing. Twenty-three patients were classified into two subgroups based on the skewing of TCRBV4. The skewing was defined to be significant if the percentage frequency of the relevant T cells was greater than 5%, and exceeded the mean percentage plus 3 s.d. of the T cells bearing the corresponding TCR in 20 healthy controls.