Low serum mannose-binding lectin levels are associated with inflammation and apoptosis in early surveillance allograft biopsies

• Low MBL levels are associated with graft inflammation in early surveillance biopsies.
• Low MBL levels are associated with macrophage-rich infiltrates in graft biopsies.
• Low MBL levels are associated with tubular cell apoptosis in graft biopsies.
• Serum MBL levels modulate renal inflammation after transplantation.

IntroductionMannose-binding lectin (MBL) is a protein of the innate immune system that participates in host defense and the tissue injury/repair process, enhancing the clearance of apoptotic cells by macrophages. The aim is to characterize the relationship between pre-transplant MBL levels, histological lesions and number of apoptotic cells in early surveillance renal allograft biopsies.Patients and methodsConsecutive renal transplant recipients were recruited and MBL levels were classified into tertiles. The first tertile was considered the low MBL group. Surveillance biopsies were done during the first 6 months and were evaluated according to Banff criteria. Renal inflammatory infiltrates were studied by immunohistochemical techniques. Apoptosis was studied using morphological methods in renal tubular cells and was expressed as the number of apoptotic cells/mm2.ResultsMBL was determined in 126 patients and a surveillance biopsy with sufficient tissue was obtained in 41 of them. Patients with low pre-transplant MBL levels showed a higher acute Banff index (3.14 ± 1.96 vs. 1.88 ± 1.56, p = 0.044) and an increased proportion of biopsies with tubular cell apoptosis The proportion of biopsies with tubular cell apoptosis was higher in patients with low pre-transplant MBL levels in comparison with patients with high MBL levels (4.3 ± 3.6 versus 0.2 ± 0.9 p = 0.012) and increased interstitial number of inflammatory cells and significantly the macrophages/mm2 (109 ± 118 vs. 32 ± 46; p = 0.04).ConclusionLow pre-transplant serum MBL levels are associated with more severe inflammation and increased apoptosis in early surveillance renal allograft biopsies suggesting that MBL modulates renal inflammation after transplantation