The ultrastructural features of peritubular capillary (PC) damage was studied in 12
kidney allografts with acute humoral rejection (AHR). AHR manifested in diffuse linear
PC staining for C4d, and histology consistent with Banff grade III in 7 recipients
and Banff grade II in 5. Allografts with acute tubular necrosis served as controls.
First biopsies (post-transplantation day 16.2 +/- 2.2): The intra-capillary exudate
comprised monocytes (59%), polymorphonuclears (14%), lymphocytes (12%) and not otherwise
specified mononuclears (15%). Three patterns of focal PC endothelial injury were observed:
lysis, an increased rate of apoptosis and fragmentation. No correlation was found
between the respective damage types and the inflammatory cell types or the Banff grades.
Controls revealed endothelial swelling, detachment from basement membrane and fragmentation.
Follow-up biopsies: Monocytes transformed into macrophages intra-luminally. The reparative
changes comprised endothelial cytoplasmic protrusions, binucleated endothelial cells
and capillary sprouts. Early transplant capillaropathy and transplant glomerulopathy
were noted in 2 recipients. Literature data indicate that lysis is mediated by anti-HLA
alloantibodies; apoptosis, demonstrated first in the present study, may be induced
by non-HLA-type anti-endothelial antibodies. Fragmentation is caused by ischemia.
Ongoing endothelial injury leads to transplant capillaropathy and transplant glomerulopathy,
the characteristic lesions of chronic rejection.
