Recently, we reported elevated proportions of circulating follicular T helper cells and higher levels of interleukin- (IL-) 21 in primary Sjögren's syndrome (pSS). Interaction of invariant natural killer T (iNKT) cells with B cells and granzyme B (GrB) production may be also important in pSS. Thirty-two pSS patients and 24 healthy controls were enrolled in our study. We investigated the expression of intracellular GrB and IL-21 receptor (IL-21R) of CD19(+)CD5(+) and CD19(+)CD5(-) B cells; furthermore, we determined the IL-21 expression of iNKT cells as well. We also assessed the proportion of transitional (CD19(+)CD24(high)CD38(high)), mature (CD19(+)CD24(int)CD38(int)) and primarily memory (CD19(+)CD24(high)CD38(-)) B cells. CD5(+) but not CD5(-) B cells showed elevated GrB and IL-21R expression in pSS; additionally IL-21 expression of iNKT cells was also elevated. The ratios of transitional and mature B cells were elevated in pSS, while primarily memory B cell percentages were decreased, which correlated with GrB and IL-21R expression of CD19(+) B cells. Our results suggest that enhanced IL-21R expression of CD19(+)CD5(+) B cells and production of IL-21 by iNKT cells may play an important role in the pathogenesis of pSS by regulating CD19(+)CD5(+) B cell functions and increasing GrB production, presumably leading to a counter-regulatory effect in the disease.