Investigation of the role of B lymphocytes and tertiary lymphoid tissue in a murine model of renal chronic allograft damage

Abstract

BackgroundNodular B-lymphocyte rich infiltrates have been identified in chronically rejected renal allografts and biopsies of acute transplant rejection, and this has been associated with the development of tertiary lymphoid tissue (TLT). However their significance is unclear, with conflicting published data. We aim to investigate the role and significance of B-lymphocyte infiltrates and the development of TLT in a murine model of renal chronic allograft damage. MethodsWe used congenic strains with donor C57bl/6-BM12 mice kidneys transplanted into C57bl/6 recipients, this being a single MHC-II mismatch. Using immunohistochemistry we investigated the presence of B lymphocytes within the allograft. In addition we investigated other markers of chronic allograft damage in this model including lymphatic expansion, microvessel rarefication, and fibrosis. FindingsNodular aggregates of B cells appearing to be TLT developed over 12 weeks; however, in some allografts we observed a scattered B-cell pattern. The B-cell infiltrate of the allograft cortex increased progressively with a significant increased density by 12 weeks compared with 5 days after transplantation. Microvessels were counted with a 25-point graticule, and there was a significant difference between allograft and native kidney cortex (p<0·01) with both time and transplant kidney being responsible for the effect. There was a significant difference in the number of lymphatic vessels at 12 and 8 weeks compared with 5 days (p<0·05). Similar to findings in chronic allograft nephropathy, the expanded lymphatics were seen both in the tubulointerstitium and in the perivascular regions. The B-lymphocyte phenotype was explored and shown by immunofluoresence to form germinal centres and IgG-positive plasma cell (CD138+) differentiation. InterpretationWe have shown that this strain combination closely models that of chronic rejection of the renal allograft. Furthermore, we have identified the progressive infiltration and expansion of the B-lymphocytes compartment within the allograft cortex. This work has provided the basis for further investigation of B-lymphocyte depletion and the prospects of identifying a regulatory B lymphocyte. FundingKidney Research UK.