NIV Congres

Introduction  Follicular T-helper cells (Thf-cells) play a pivotal role in the differentiation of B-lymphocytes into antibody secreting cells, i.e. plasmablasts (CD19+CD20-CD27+CD38++). CD4+CXCR5+ T-cells are their peripheral blood counterparts and share functional properties with Thf-cells. They comprise IFNγ, IL17 and IL21 producing cells. B-cell mediated alloreactivity has been recognized as common cause of allograft dysfunction and predicts both early and late graft loss. Here we examined the frequency and functions of peripheral Thf-cells critical for B-cell activation before and after kidney transplantation (Tx).

Methods Peripheral blood samples of patients (N=30) before and after kidney Tx and of healthy controls (N=16) were studied. Patients were treated with Tacrolimus, MMF and steroids. By flow cytometry the absolute numbers of CD4+CXCR5+ T-cells, and their cytokine producing profile (IL17, IL21 and IFNγ) as well as the numbers of plasmablasts were measured. Functional interaction was studied by co-culture experiments (N=6) of cell sorted CD4+CXCR5+ and CD4+CXCR5- T-cells with sorted endotoxin activated B-cells. B-cell differentiation and IgM and IgG production were determined in the presence and absence of Tacrolimus (10 ng/ml).  

Results Before Tx the absolute numbers of CD4+CXCR5+ T-cells were significantly lower than in healthy controls, and these numbers remained stable after Tx. However, after Tx the IL21 and IFNγ, but not the IL17 production capacity by the CD4+CXCR5+ T-cells was significantly reduced compared to before Tx (both p<0.01). Moreover, patients had a significantly lower plasmablast count than healthy controls (p<0.02). Interestingly, after Tx a complete vanishing of plasmablasts was observed (p<0.0001). The co-cultures studies revealed that only CD4+CXCR5+ T-cells, but not CD4+CXCR5- T-cells, provided help to B-cell differentiation into IgM and IgG producing plasmablasts (p<0.05). This CXCR5+ dependent T-cell help to B-cells was completely inhibited by Tacrolimus. Differentiation of B-lymphocytes into plasmablasts was highly correlated with IgM and IgG production, R_s=0.91, p<0.0001 and R_s=0.85, p<0.0001, respectively.

Conclusion We showed that the functionality of peripheral Thf-cells (CD4+CXCR5+), critical for the B-cell mediated immunity, is inhibited in kidney transplant patients. Moreover, Tacrolimus completely blocked B-cell differentiation into Ig secreting plasmablasts.