Smedbråten et al. BMC Nephrology (2016) 17:148 DOI 10.1186/s12882-016-0373-9 RESEARCHARTICLE Open Access Low level of MAp44, an inhibitor of the lectin complement pathway, and long-term graft and patient survival; a cohort study of 382 kidney recipients Julia Smedbråten1,2* , Geir Mjøen3, Anders Hartmann2,3, Anders Åsberg3,4,5, Halvor Rollag2,6, Tom Eirik Mollnes2,7,8,9, Leiv Sandvik10, Morten W. Fagerland10, Steffen Thiel11 and Solbjørg Sagedal1 Abstract Background: Higher incidence of malignancy and infectious diseases in kidney transplant recipients is related to immunosuppressive treatment after transplantation and the recipient’s native immune system. The complement system is an essential component of the innate immunity. The aim of the present study was to investigate the association of effector molecules of the lectin complement pathway with graft and patient survival after kidney transplantation. Methods: Two mannan-binding lectin (MBL) associated proteases, MASP-2 and MASP-3 (activators of the lectin pathway) and two MBL-associated proteins, MAp44 and MAp19 (inhibitors of the lectin pathway) were measured at the time of transplantation in 382 patients (≥17 years old) transplanted in 2000–2001. The cohort was followed until December 31, 2014. Data on patient and graft survival were obtained from the Norwegian Renal Registry. Cox proportional hazard regression models were performed for survival analyses. Results: Low MAp44 level (1st versus 2–4 quartile) was significantly associated with overall mortality; HR 1.52, 95 % CI 1.08–2.14, p = 0.017. In the sub analyses in groups below and above median age (51.7 years), low MAp44 as a predictor of overall mortality was statistically significant only in recipients of ≤51.7 years; HR 2.57, 95 % CI 1.42–4.66, p =0.002. Furthermore, low MAp44 was associated with mortality due to infectious diseases; HR 2.22, 95 % CI 1.11–4.41, p =0.023. There was no association between MASP-2, MASP-3 or MAp19 levels and patient mortality. No association between any measured biomarkers and death censored graft loss was found. Conclusions: Low MAp44 level at the time of transplantation was associated with increased overall mortality in kidney recipients of median age of 51.7 years or below and with mortality due to infectious diseases in the whole patient cohort after nearly 14-years of follow up after transplantation. No associations between other effector molecules; MASP-2, MASP-3 or MAp19 and recipient mortality were found, as well as no association of any biomarker with death censored graft loss. Keywords: Kidney transplantation, Complement, Recipient survival * Correspondence: [email protected] 1Department of Nephrology, Ullevål Oslo University Hospital, Postbox 4950Nydalen, 0424 Oslo, Norway 2Faculty of Medicine, University of Oslo, Oslo, Norway Full list of author information is available at the end of the article © 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Smedbråten et al. BMC Nephrology (2016) 17:148 Page 2 of 9 Background at the time of transplantation were available in 382 of Kidney transplantation is the treatment of choice for the patients, who were included in the present study. In end-stage kidney disease, providing patients with a bet- the present study the follow up period was extended ter quality of life and reducing overall morbidity. Despite until December 31, 2014. Data on patient survival was this, kidney transplant recipients have higher mortality obtained from the Norwegian Renal Registry. Prophylaxis compared to the general population. The effectiveness of with trimethoprim-sulfamethoxazole against Pneumocystis the adaptive immune system begins to diminish already jiroveci was routinely used for 6 months after transplant- with progression of chronic kidney disease. An observed ation. No patients received prophylaxis against cytomegalo- increased incidence of malignancy [1] and infectious virus (CMV) but were treated with valganciclovir at first diseases [2] after transplantation could be related both positive CMV antigen test. to immunosuppressive treatment after transplantation and to the state of the recipient’s immune system. Immunosuppressive treatment The complement system is an essential component of The immunosuppressive regimen was routinely based on the innate immune system. It plays an important role in a calcineurin inhibitor, except for five patients with anti-microbial defense processes such as immunological haemolytic uraemic syndrome who received sirolimus. response to pathogens, but it is also involved in At that time the induction therapy was not included in inflammatory processes such as ischemia reperfusion the standard immunosuppression protocol. Calcineurin injury, transplant immunity, auto-immune diseases, co- inhibitors were combined with either mycophenolate agulation [3–5] and probably in development of diabetic mofetil (MMF) or with induction therapy. Altogether angiopathy [6]. The complement system can be activated 161 patients (42 %) received induction with basiliximab through the classical, the lectin and the alternative path- (Simulect®), and in one patient anti-thymocyte globulin ways, which are described in details elsewhere [7]. The was used as induction therapy. The remaining 220 lectin pathway of the complement system is activated patients (58 %) received MMF. Only 13 patients received when pattern recognition molecules (PRMs), including quadruple immunosuppression with basiliximab, calcine- the two collectins (mannan-binding lectin (MBL) and urin inhibitors, MMF and steroids. Azathioprine in collectin-LK (CL-LK)) and the three ficolins (ficolin-1, combination with cyclosporine and steroids was given ficolin-2 and ficolin-3) bind to a fitting pattern on only to three patients. Except for ten patients who microorganisms or on altered tissues. When this occurs participated in the ATLAS trial and followed a steroid three MBL-associated proteases (MASP-1, MASP-2 and free protocol [11], all patients received steroids. MASP-3) provide activation of the complement system and two MBL-associated proteins (MAp44 and MAp19) Biochemical assays serve as natural endogenous competitive inhibitors [7, 8]. MASP-2. The MASP-2 assay was previously described in MASP-1, MASP-3 and MAp44 arise from the MASP1 detail [12]. Microtiter wells were coated with 0.5 μg gene by mutually exclusive splicing [9]. In a similar man- anti-MASP-2 antibody (MAb clone 8B5) in 100 μl PBS ner MASP-2 and MAp19 arise from the MASP2 gene [7]. overnight at 4 °C. The wells were blocked and washed Our hypothesis is that the activity of the native with buffer. The samples were diluted 75-fold in 1 M immune system plays an important role in the transplant NaCl, 10 mM Tris–HCl, 10 mM EDTA, 15 mM NaN3, population given the reduced activity in the adaptive 0.05 % (v/v) Tween 20, pH 7.4, containing 0.01 % (w/v) immune system due to immunosuppressive treatment. heat aggregated human IgG (Beriglobin, incubated The aim of this study was to investigate whether the sta- 30 min at 63 °C and centrifuged 10 min at 3000 g to tus of the lectin pathway at the time of transplantation remove large aggregates). The heat aggregated human may influence long term kidney graft and patient sur- IgG is included to inhibit the influence of possible vival. The lectin pathway was investigated by measuring rheumatoid factors in sandwich type immuno assays. A levels of activators like MASP-2 and MASP-3 and of the pool of plasma was used as a standard and three differ- regulatory molecules MAp44 and MAp19, and by evalu- ent plasma samples were used as internal controls and ating a possible correlation between levels of MASP-3 included on each microtiter plate used. Following and MAp44 or between MASP-2 and MAp19. incubation overnight at 4 °C, the wells were washed and incubated for 1.5 h at room temperature with 0.1 μg Methods biotinylated anti-MASP-2 antibody (MAb 6G12), in Study population 100 μl of TBS/Tw/CaCl2 (10 mM Tris–HCl, 145 mM A cohort of 402 adult kidney graft recipients (≥17 years), NaCl, 5 mM CaCl2, 15 mM NaN3, 0.05 % (v/v) Tween transplanted in 2000 and 2001 at Oslo University 20, pH 7.4) containing 0.01 % (w/v) heat aggregated Hospital Rikshospitalet, was included in the original human IgG and 1 % (v/v) bovine serum. The wells were study previously described in detail [10]. Blood samples washed followed by incubation with 10 ng europium- Smedbråten et al. BMC Nephrology (2016) 17:148 Page 3 of 9 labelled streptavidin (Perkin Elmer) in 100 μl of TBS/ acetate buffer (50 mM Na-acetate, 145 mM NaCl, Tw, 25 μM EDTA for 1 h at room temperature. After pH 4.5) o.n. at 4 °C. The wells were then blocked with wash bound europium was detected by time-resolved HSA, 1 mg/ml TBS, washed thrice with TBS/Tw, and fluorometry after the addition of an enhancement incubated o.n. at m temperature with serum samples solution (Perkin Elmer). diluted 20-fold in MAp19 buffer (10 mM Tris–HCl, 1 M MASP-3. The MASP-3 assay we used was described in NaCl, 10 mM EDTA, 0.05 % Tween 20) containing details by Degn et al. [9]. Microtiter wells were coated 100 μg heat-aggregated hIgG per ml, and 100 μg normal with 0.2 μg antibody reacting with MASP-3 (MAb 5F5) rat IgG per ml. After washing the wells, biotinylated in 100 μl PBS overnight at 4 °C.