Incidence of C4d Staining and Morphology of Acute Humoral Rejection in Protocol Biopsies of Renal Allografts: A Multicenter Study.

Objective: C4d staining in peritubular capillaries (PTC) has been established as an in situ marker of humoral rejection. A definite cut-off for the C4d stain is still under discussion. Few data are available about the incidence of C4d deposition in protocol biopsies (Bx) in comparison to that of indicated biopsies. To test whether center specific factors are influencing the incidence of C4d detection we performed a multicenter study. Methods: Bx were from Hannover, Germany, Barcelona, Spain, and Antwerp, Belgium. 779 paraffin embedded biopsies (501 protocol, 278 indication) were stained by immunohistochemistry using a polyclonal antiserum. C4d results in PTC were recorded in five groups: >50% of PTC/biopsy core area C4d positive, 25-50%, 5-25%, >5%, C4d negative. Staining results were correlated to clinical data. Bx were classified following the updated Banff 2001 criteria. Additionally, the amount of inflammatory cells in PTC were graded according to a proposal made at the recent Banff 2003 meeting. Results: Diffuse C4d deposition (>50% of PTC) was found in 1.6% of protocol Bx and in 11.2% of indication Bx. The incidence in protocol Bx varied from 0.8% to 6.4% between the different centers. A focal C4d stain (25-50% of PTC) was found in 2.0% of protocol Bx and 8.6% of indication Bx. Diffuse C4d staining is more frequent in females, in patients with pre-transplants, or PRA >30%. Inflammatory cells in PTC and acute tubular injury are the most common morphological findings in C4d positive cases. Conclusions: The incidence of C4d staining in protocol Bx is lower than in indication Bx. Diffuse C4d deposition in PTC accompanied by morphological signs of AHR occur in stable renal allografts, suggesting subclinical AHR. Focal C4d detection seems to be related to morphological signs of AHR, too. [ABSTRACT FROM AUTHOR]