Renal interstitial mast cell counts differ across classes of proliferative lupus nephritis

Systemic lupus erythematosus frequently involves the kidneys leading to significant morbidity and mortality. It is classified according to glomerular involvement pattern but tubulointerstitial lesions are also important for progression and prognosis, as seen in other kidney glomerular diseases. One of the cell types which participate in this process are mast cells. The aim of the study was to analyze the counts of tryptase-positive and chymase-positive mast cells in lupus nephritis classes II, III and IV. Material consisted of 42 renal biopsies from patients with lupus nephritis; 11 class II, 9 class III and 22 class IV. Chymase- and tryptase-containing cells were stained by immunohistochemistry and counted microscopically. Mean count of chymase-positive mast cells was 9.8/10 high power fields (hpf) for the whole group, 4.66 for class II, 11.89 for class III, and 11.51 for class IV. The mean count of tryptase-positive cells was 18.6/10 hpf for the whole group, 7.65 for class II, 25.57 for class III, and 21.23 for class IV. The differences between lupus nephritis classes were significant both for chymase- and tryptase-positive cells. Tryptase- but not chymase-positive cell counts showed a correlation with the creatinine level (R = 0.35). These results suggest that mast cells are involved to a different degree in the pathogenesis of lupus nephritis depending on the class of the disease.