TLR10 expression in B cells in pSS patients
Both previous studies [12, 13] and the Human Protein Atlas showed that TLR10 mRNA mainly enriched in B cells, less in dendritic cells and monocytes, and undetectable in other peripheral blood immune cells. Therefore, to investigate the differences in TLR10 expression on the B cell surface between pSS patients and HCs, we isolated PBMC from the above two groups and detected them by flow cytometry. The proportion of CD19+ B cells in PBMC between pSS patients and HCs was comparable (Sup. Fig. 1). Compared with the HCs, the pSS patients expressed relatively high levels of TLR10 on CD19+ B cells’ surface when determined by the mean fluorescence intensity (MFI) (Fig. 1a-b), but there were no statistical differences between the two groups. In addition, the proportion of TLR10+CD19+ B cells was also similar between the two groups (Fig. 1c-d).
Correlation between TLR10 expression in B cells and pSS related autoantibodies
Anti-SSA, anti-SSB, and anti-Ro52 are important clinical diagnostic indicators for pSS patients, and their concentrations are usually positively correlated with pSS progression [21–23]. We analyzed the TLR10 expression in B cells in pSS patients according to the extractable nuclear antigen profile results. Interestingly, the expression of TLR10 in CD19+ B cells from anti-SSA+++ and anti-Ro52+++ pSS patients is significantly reduced as compared with the anti-SSA−/+ and anti-Ro52+/− pSS patients respectively (Fig. 2a-b), and anti-SSB+++ pSS patients show a moderate reduction in TLR10 expression as compared with anti-SSB−/+ pSS patients (Fig. 2c), indicating that the expression of TLR10 in B cells might be related with the production of autoantibodies in pSS patients. Further ELISA results showed that the expression of TLR10 in CD19+ B cells is negatively correlated with serum level of anti-SSA (r = -0.4599, p = 0.0138), anti-SSB (r = -0.4028, p = 0.0336) and ANA (r = -0.7855, p = 0.0011) in pSS patients (Fig. 2d-f). Moreover, the expression of TLR10 in CD19+ B cells was negatively correlated with BAFF (r = -0.4092, p = 0.0306) (Fig. 2g), which is important for survival and activation of B cells and presents excessive level in pSS patients [24]. These results suggested that the expression of TLR10 in CD19+ B cells might be correlated with pSS formation and/or progression.
TLR10 expression is mainly upregulated in switched memory B in pSS
Numerous studies have been reported that memory B cells, PB, and plasma cells are the key subsets of B cells involved in the pathogenesis of pSS [4]. We further analyzed the expression of TLR10 in peripheral B cell subsets, including CD19+CD24++CD38++ transitional B cells, CD19+IgD+CD27− naïve B cells, CD19+CD27+ memory B cells, CD19+IgD+CD27+ unswitched memory B cells, CD19+IgD−CD27+ switched memory B cells, and CD19+CD24−CD38++ PB (Fig. 3a), obtained from both the pSS patients and HCs. The results showed that TLR10 expression was similar between the pSS patients and HCs in transitional B cells, naïve B cells, memory B cells, unswitched memory B cells, and PB (Fig. 3b). Interestingly, the expression of TLR10 in switched memory B cells was significantly increased in pSS patients compared with the HCs (Fig. 3b). Moreover, the expression of TLR10 in memory B cells and switched memory B cells was negatively correlated with serum level of anti-SSA (memory B, r = - 0.4034, p = 0.0333; switched memory B, r = -0.3953, p = 0.0373) and BAFF (memory B, r = -0.3966, p = 0.0367; switched memory B, r = -0.3760, p = 0.0486) in pSS patients (Fig. 3c-f), respectively. The expression of TLR10 in memory B cells and switched memory B cells showed no significant correlation with the serum level of anti-SSB (memory B, r = -0.2288, p = 0.2416; switched memory B, r = -0.2376, p = 0.2234) in pSS patients (Sup Fig. 2a-b). In addition, the expression of TLR10 in transitional B cells, naïve B cells, unswitched memory B cells, and PB showed no obvious correlation with serum level of anti-SSA, anti-SSB, and BAFF in pSS patients, respectively (Sup Fig. 2c-e). These results further confirmed that the expression of TLR10 was increased in switched memory B cells, which might play an important role in pSS progression.
TLR10 expression in B cells is negatively correlated with pSS progression
Although TLR10 expression in CD19+ B cells showed no significant differences between the HCs and pSS patients, we wondered that whether TLR10 expression in B cells changed with pSS progression. Firstly, the expression of TLR10 in B cells in pSS patients with low- and high-activity evaluated by ESSDAI according to their clinical features[20] was analyzed by flow cytometry. As shown in Sup Fig. 3a, the proportion of CD19+ B cells among the HCs, low- and high-activity pSS patients was comparable. Interestingly, the expression of TLR10 in CD19+ B cells in low-activity pSS patients significantly increased compared with the HCs, while decreased in high-activity pSS patients compared with low-activity pSS patients (Fig. 4a). Then we divided the pSS patients into TLR10 high- and low-expressed groups based on the average value of the TLR10 MFI of CD19+ B cells, and calculated the proportion of low- or high-activity patients between the two groups. As shown in Fig. 4h, the proportion of high-activity patients in TLR10 low-expressed pSS patients was significantly higher than that in TLR10 high-expressed pSS patients (76.19% vs 7.69%). Conversely, the proportion of low-activity patients in TLR10 low-expressed pSS patients was significantly lower than that in TLR10 high-expressed pSS patients (23.81% vs 92.31%). Moreover, correlation analysis showed that the pSS progression was closely related to TLR10 expression in CD19+ B cells (p <0.001) (Table 2). These results suggested that TLR10 expression in CD19+ B cells was negatively correlated with pSS progression.
Table 2
Relationship between TLR10 expression and pSS progression
| Low-activity (n) | High-activity (n) | P-value* |
TLR10-low expressed | 5 | 16 | <0.001 |
TLR10-high expressed | 12 | 1 |
*Chi-Square Test and Fisher’s exact Test were used. |
TLR10 expression in naive and memory B cells is upregulated in low-activity pSS patients
To clarify whether the TLR10 expression in B subsets changed during the pSS progression, we analyzed the expression of TLR10 in peripheral B subsets in the HCs, low- and high-activity pSS patients. Compared with the HCs, the high-activity pSS patients presented with a significantly increased proportion of transitional B cells, naive B cells, and PB proportion, respectively, but decreased proportion of memory B cells, as well as unswitched and switched memory B cells (Sup. Fig. 3b-g). Consistent with the above results, the expression of TLR10 in transitional B cells and PB was relatively comparable among these groups (Fig. 4b and g). Notably, the expression of TLR10 in naïve B cells, memory and switched memory B cells was increased in low-activity pSS patients compared with the HCs (Fig. 4. c, d, and f). With the progression of pSS, the expression of TLR10 in naïve and memory (including unswitched and switched) B cells was significantly decreased in high-activity pSS patients compared with low-activity pSS patients (Fig. 4c-f). These results suggested that TLR10 expression might suppress pSS progression by taking part in the process of B cell activation and differentiation.