MAST-CELLS IN ACUTE CELLULAR REJECTION OF HUMAN RENAL-ALLOGRAFTS

Mast cells (MCs), few in the normal kidney, are found in increased num ber in the renal parenchyma in diseases associated with persistent chr onic inflammation. MCs are not easily identified in routinely processe d archival tissue sections with histochemical stains. A more reliable method of detection was provided with the introduction of MC tryptase- specific monoclonal antibodies. To determine the possible role of MCs in renal allograft rejection, we studied 28 biopsy specimens from rena l allografts that had been in place for various lengths of time (from 3 days to 40 months) in patients whose primary diagnosis was acute int erstitial rejection; die specimens were associated with varying degree s of interstitial fibrosis, edema, and hemorrhage. The specimens were graded on a semiquantitative scale (from 0 to 3+) for the severity of rejection, the degree of interstitial fibrosis, interstitial edema, an d interstitial hemorrhage. Eosinophils, plasma cells, and MCs were qua ntitatively evaluated in these biopsy specimens. MCs were detected by use of a commercially available anti-MG tryptase monoclonal antibody, which proved to be an excellent tool to detect MCs in routinely proces sed paraffin sections. A positive correlation was found between the nu mber of MCs and the time since transplantation (R = 0.841, P < 0.005) and between the number of MCs and the severity of interstitial fibrosi s (R = 0.489, P < 0.005), as well as with interstitial edema (R = 0.51 7, P < 0.005). MCs were increased in number in patients with moderate (n = 18; mean, 18.00 MCs per 10 high power fields [HPFs]) and severe ( n = 5; mean, 12.20 MCs per 10 HPFs) acute rejection compared with pati ents with mild (n = 5; mean, 2.44 MCs per 10 HPFs) acute rejection and normal kidneys (n = 6; mean, 1.75 MCs per 10 HPFs). These results sug gested that MCs might play a role in the process of acute rejection of renal allografts and in the development of interstitial fibrosis.