Quantitative analysis of interstitial mast cells in AA and AL renal amyloidosis.

Eighteen renal biopsy specimens obtained from patients with AA-type renal amyloidosis (AA) and 11 from patients with AL-type renal amyloidosis (AL), for whom both light and electron microscopy as well as immunofluorescence microscopy and full clinical data were available, were examined quantitatively. The cases were selected on the basis of immunohistochemical studies. As a control, we used 10 biopsy specimens from the kidneys removed because of trauma. Morphometric investigations were carried out by a computer image analysis system to find an answer to the question of whether mast cells can correlate with tubulointerstitial fibrosis in AA and AL renal amyloidosis, and to examine the relationship between mast cells and interstitial alpha-smooth muscle actin (alpha-SMA) expression and interstitial infiltrates. The morphometric study revealed that the mean values of the interstitial tryptase-positive cells, expression of alpha-SMA, interstitial volume, CD68+, CD45RB+, CD43+ and CD20+ cells were increased in AA as compared with the AL group, most of them significantly. Most of these parameters were also significantly increased in both AA and AL patients as compared with the control group. In both the AA group and the AL group, there existed some significant positive correlations between interstitial tryptase-positive cells and interstitial expression of alpha-SMA, interstitial volume and CD68+ cells. Interestingly, in AA cases, but not in AL cases, we noted a significant relationship between interstitial tryptase-positive cells and CD43+ cells. Our findings demonstrate that mast cells belong to the constitutive cell types in the interstitium in renal amyloidosis, in particular in amyloid type A. In addition, in both the AA group and the AL group, the significant positive correlations between interstitial mast cell count and relative interstitial volume and interstitial expression of alpha-SMA suggest that these cells play a role in the development of interstitial fibrosis.