C4d - staining: Comparison of methods C. Seemayer, A. Gaspert, M. Mihatsch
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C4d - staining: Comparison of methodsC. Seemayer, A. Gaspert, M. Mihatsch
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Introduction
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Tx-Normal
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Detection of C4d:
Frozen sections, mAb QuidelParaffin sections:C4dpAb, Biomedica
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Comparison of results by 2 investigators
Renal allograft biopsies
Frozen sections
Formalin fixation
Paraffin sections
Indirect IF
Mouse monoclonal anti-C4d antibody
IHC with ABC method
Rabbit polyclonal anti-C4d antibody
Cryo-conservation
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Aim of the study:1.Comparison of frozen to frozen biopsies with respect to time-dependent stability and investigator dependent reproducibility of results
2.Comparison of F-IF and corresponding P-IHC staining patterns
3.Investigation of P-IHC staining patterns focusing on the inter- and intra-observer variability
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Materials & Methods (1)
Patients and biopsies
– retrospective study – 64 kidney allograft Bx (Basel 1996 - 2004)– parallel Bx cores either frozen or formalin fixed– 240 renal allografts Bx (50 different units)– independent analysis by two renal pathologists
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Materials & Methods (2)
Immunofluorescence
– snap frozen tissues – indirect IF technique – 1st ab: mouse anti-human anti-C4d antibody – dilution 1:50– Quidel (San Diego, CA, USA)– 2nd ab: Alexa-Fluor 488-labeled goat anti-mouse IgG – dilution 1:200
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Materials & Methods (3)
Immunhistochemistry
– formalin fixed and paraffin embedded tissue sections– rabbit polyclonal antibody – anti-C4dpAb (Biomedica, Vienna, Austria)– antigen: split product C4d (aa 1252-1256 of C4) – dilution 1:10 and 1:20– heat antigen retrieval– ABC Elite complex method
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Materials & Methods (4)
Evaluation / Scoring
– Diffuse expression: > 50% of PTC positive– Focal expression: 10 PTC < 50% of PTC positive – Focal minimal expression: 3 - 10 PTC positive – Negative: < 3 PTC or completely negative
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Results
Qualitative differences between frozen and paraffin sections
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Staining patterns for C4d in frozen and paraffin sections
C4d in frozen sections C4d in paraffin sections
Specific staining in normal kidneys
Glomerular mesangium and less severe peripheral BM
Not present
Diagnostic staining in transplants
Linear staining of cortical PTC in unscared areas
Linear staining of cortical PTC in unscared areas
Special findings in cases with PTC positivity
Often stronger staining in PTC of the medulla than in the cortexStrong staining in areas of fibrosis and tubular atrophyStronger staining of glomeruli
Special findings in diseased kidneys
Strong staining of glomerular BM in case of glomerular damageProtein deposits in arteriolar hyalinosis (common) Thickened tubular BM (rare)
Staining of unknown specificity Endothelium of arteriesStaining of plasma in capillaries In some cases strongly staining granules along PTC making inrerpretation sometimes impossibleProtein droplets in tubular cellsCellular interstitial infiltratesa
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Results
1.Comparison of frozen to frozen biopsies with respect to time-dependent stability and investigator dependent
reproducibility of results
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Results
1. Comparison of F-IF and correspondingP-IHC staining patterns
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Overall comparison of C4d expression in frozen (IF) and formalin fixed (IHC) sections
No. of cases
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Comparison of C4d expression in diffuses cases frozen (IF) versus paraffin embedded (IHC)
0
5
10
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20
25
30
D (IF) D F FM Neg
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Comparison of C4d expression in focal cases frozen (IF) versus paraffin embedded (IHC)
0
5
10
15
20
25
F (IF) D F FM Neg
No. of cases
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Comparison of C4d expression in focal mini cases frozen (IF) versus paraffin embedded (IHC)
0
1
2
3
4
5
6
7
FM (IF) D F FM Neg
No. of cases
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Comparison of C4d expression in negative cases frozen (IF) versus paraffin embedded (IHC)
0
2
4
6
8
10
Neg D F FM Neg
No. of cases
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Number of PTC expressing C4d in diffuse cases: frozen (IF) versus paraffin embedded (IHC)
% of C4d PTC
IF IHC
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Investigator dependent variability :Frozen (IF2) versus paraffin in investigator 1 / 2
Type of comparison Compared item Kappa-value
Frozen to paraffin Investigator 1
antibody-dilution 1:10 1:20
0.340.29
Investigator 2antibody-dilution 1:10 1:20
0.320.27
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Inter- and intra-investigator dependent variability in paraffin: Investigator 1 / 2 and antibody
dilutions 1:10 / 1:20
Type of comparison Compared item Kappa-value
Paraffin to paraffin Investigator 1 / 21:101:20
0.570.63
Intra-observer (Inv.2)1:101:20
0.680.83
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Conclusion
C4d staining results reported on frozen tissue samples using IF with a monoclonal antibody appear to be better suited for diagnostic as well as research purposes.
Future studies should correlate C4d staining patterns with circulating donor specific antibodies.
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Unanswered Questions– Grading: negative, focal and diffuse
– Significance of C4d in glomeruli
– Co- staining of C4d and other complement factors
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Take Home Message
1. C4d in PTC is a footprint of a humoral immune response:Search for donor specific Ab
2. Tx-glomerulitis, Tx endarteritis, leukocytes in PTC are the most important morphological indicators of humoral rejection:Search for C4d
3. Use -whenever possible- frozen sections for the detection of C4dFocal deposits in frozen sections may be lost in paraffin sections due to lower sensitivity of the method.
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Open Questions
– Clinical significance of focal deposits of C4d in PTC
– Clinical and biological significance of late C4d deposits (after years)
– Is the „dose“ of antibodies relevant for the morphological sequelae?
– Why are donor specific antibodies not always associated with C4d deposits?
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– Why is the morphology so variable in C4d positive cases?
– Why is only C4d present and no other complement components?
– Is the effect of antibodies against HLA Class I the same as against Class II?
– Pathogenesis of Tx-glomerulitis and Tx-endarteritis without C4d deposits.
Open Questions