Comparison of Infiltrating T Cells, B Cells and Macrophages During Experimental Renal Allograft Rejection

Abstract

Despite substantial improvement of modern immunosuppression and reduced rejection rates, acute rejection still remains an obvious clinical problem after kidney transplantation. Acute rejection represents an ongoing immunological risk factor for subsequent interstitial fibrosis and tubular atrophy, whereby acute rejection scored on basis of the Banff classification focuses on the degree of lymphocyte infiltration to the interstitium, tubuli and arterial vessels. However, for the histological grading of acute rejection the specific subtypes of infiltrating cells are not considered. We performed an experimental renal transplantation model (Brown-Norway to Lewis) as standardized data on the infiltration pattern of CD3 positive T-cells, CD68 positive macrophages and CD20 positive B-cells after kidney transplantation are missing. We examined the dynamics of above named infiltrating cell populations 6 and 28 days after allogeneic transplantation. These data were compared with syngeneic transplanted rats and control rats. Cyclosporine A was administered as immunosuppression (5 mg/kg bw/day) and trough levels were comparable to clinical practice in humans. The expression of infiltrating cells was evaluated in interstitial, perivenous, periarterial, periglomerular and intraglomerular regions of kidney allografts under light microscope and was on the other hand analyzed by two different morphometric software programs. Resulting data were correlated with the corresponding kidney function as well as with histopathological classification according to Banff. In CsA treated control rats there was nearly no positive staining for CD3, CD20 and CD68 in the different compartments. Whereas the morphometric software based analysis of syngeneic transplanted rats demonstrated only a moderate 4-fold increase in CD4, a 1.6-fold increase in CD20 and a 5.4-fold increase in CD68 infiltration in comparison with control rats, a tremendous increase was seen in allogeneic transplanted rats in all infiltrating cell populations. The relative increase in CD20 infiltration (57-fold induction) was even more pronounced than the increase in CD3 (20.5-fold induction) or CD68 (5.4-fold induction) infiltration. 28 days after allogeneic transplantation, the number of infiltrating cells was still significantly increased, but to a lower extend than on day 6. The expression profile of infiltrating cells in the different cellular compartments was in accordance with the morphometric analysis. In conclusion, we established a highly standardized experimental model of renal transplantation to study the infiltrating patterns of CD3, CD20 and CD68 positive cells. After allogeneic transplantation we demonstrated a significant induction of CD3, CD20 and CD68 positive cells. The amount of infiltrating cells and the detailed localization of the infiltrating cells in different kidney compartments were evaluated for the first time with different immunohistochemical analyzing methods. Besides infiltration of CD3 and CD68 infiltrating cells, the robust infiltration of CD20 B-cells, even at early time points after transplantation might act as a silent subclinical trigger for subsequent chronic humoral rejection and premature graft loss.