Kinetics of human B cell behavior and amplification of proliferative responses following stimulation with IL-21

Although recent studies indicated that IL-21 is an important regulator of human B cell activation, detailed comparison of the effects of IL-21 on distinct B cell subsets have not been performed. Our studies revealed that IL-21R is expressed by naive and germinal center B cells, but not memory or plasma cells. IL-21R was increased on naive and memory B cells following in vitro activation. Investigation into the kinetics and magnitude of responses of human B cells to IL-21 revealed that IL-21 potently augmented proliferation of CD40L-stimulated neonatal, splenic naive, and memory and tonsil germinal center B cells. This response exceeded that induced by IL-4, IL-10, and IL-13, cytokines that also induce B cell proliferation. Remarkably, CD40L/IL-21-stimulated naive B cells underwent the same number of divisions as memory cells and exhibited a greater enhancement in their response compared with CD40L alone than memory B cells. Therefore, IL-21 is a powerful growth factor for naive B cells. This may result from the higher expression of IL-21R on naive, compared with memory, B cells. Stimulation of human B cells with CD40L/IL-21 also induced IL-10 production and activation of STAT3. We propose that IL-21 may have therapeutic application in conditions of immunodeficiency where it could expand naive B cells, the predominant B cell subset in such patients. Conversely, because IL-21 is increased in murine models of lupus, dysregulated IL-21 production may contribute to perturbed B cell homeostasis observed in systemic lupus erythematosus. Thus, antagonizing IL-21 may be a novel strategy for treating Ab-mediated autoimmune diseases.

Control of matrix metalloproteinase production in human intestinal fibroblasts by interleukin 21

BACKGROUND

T cell-mediated immunity plays a central part in the pathogenesis of tissue damage in inflammatory bowel disease (IBD). The mechanism by which T cells mediate tissue damage during IBD remains unclear, but evidence indicates that T cell-derived cytokines stimulate fibroblasts to synthesise matrix metalloproteinases (MMPs), which then mediate mucosal degradation. We have previously shown that, in IBD, there is high production of interleukin (IL) 21, a T cell-derived cytokine, which enhances Th1 activity.

AIM

To investigate whether IL21 controls MMP production by intestinal fibroblasts.

METHODS

IL21 receptor (IL21R) was evaluated in intestinal fibroblasts by reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting. Fibroblasts were stimulated with IL21 and MMPs were evaluated by RT-PCR and western blotting. The effect of a neutralising IL21R fusion protein (IL21R/Fc) on the induction of MMPs in fibroblasts stimulated with IBD lamina propria mononuclear cell (LPMC) supernatants was also evaluated.

RESULTS

Intestinal fibroblasts constitutively express both IL21R and the common gamma chain receptor, which are necessary for IL21-driven signalling. IL21 enhances fibroblast production of MMP-1, MMP-2, MMP-3 and MMP-9, but not tissue inhibitors of MMP-1 and MMP-2. Moreover, IL21 synergises with tumour necrosis factor alpha to increase synthesis of MMP synthesis. IL21 enhances MMP secretion without affecting gene transcription and protein synthesis. IBD LPMC supernatants stimulate MMP secretion by intestinal fibroblasts, and this effect is partly inhibited by IL21R/Fc.

CONCLUSIONS

These results suggest that fibroblasts are a potential target of IL21 in the gut and that IL21 controls MMP secretion by fibroblasts.