C4d Complement Split Product in Diagnosis of Immunological Activity of Chronic Allograft Nephropathy

The use of C3d and C4d immunohistochemistry on formalin-fixed tissue as a diagnostic adjunct in the assessment of inflammatory skin disease

BACKGROUND

Direct immunofluorescent (DIF) testing defines an important diagnostic adjunct in the classification of various inflammatory skin conditions; it requires fresh tissue, a laboratory equipped to perform the procedure, and a pathologist skilled in its interpretation. Although advances have been made in the development of antibodies that can be applied to paraffin-embedded tissue, there has been no reported success on the application of paraffin tissue-based immunohistochemistry as a potential substitute for DIF testing on skin biopsy material.

OBJECTIVE

We applied C3d and C4d immunohistochemistry on paraffin-embedded, formalin-fixed tissue to define a potential application of these two antibodies as a diagnostic adjunct in the evaluation of various inflammatory skin diseases.

DESIGN

A natural language search identified cases submitted for both light microscopic and DIF studies from July 2006 to August 2007. We prospectively included similar cases encountered from August 2007 to March 2008. We correlated the C3d and C4d staining pattern with the DIF and light microscopic findings.

RESULTS

All cases of scarring discoid lupus erythematosus (LE) (20/20) and systemic LE (5/5) showed prominent granular C3d along the dermoepidermal junction (DEJ) and a positive lupus band test result in the latter by DIF. All systemic LE cases demonstrated granular DEJ C4d with C3d or C4d in blood vessels (BV). There was a negative lupus band test result without DEJ C3d or C4d in all cases of subacute cutaneous lupus erythematosus (SCLE) (15/15). There were, however, deposits of C4d within epidermal keratinocytes (7/7), corresponding to IgG decoration of keratinocytes by DIF and the presence of anti-Ro antibodies. Dermatomyositis cases showed prominent mural C3d and C4d in BV corresponding to C5b-9 by DIF (12/12) and one case of hydroxyurea-induced dermatomyositis lacked this staining. Although by DIF all dermatomyositis cases had a negative lupus band test result, 25% of cases showed staining for C3d along the DEJ (3/9). Bullous pemphigoid cases demonstrated homogenous DEJ C3d (17/17) whereas C4d was characteristically negative; there was 100% concordance with linear IgG and C3d by DIF. Eighty two percent of pemphigus cases demonstrated prominent intercellular C3d and C4d, roughly mirroring the intercellular pattern for IgG and complement seen by DIF (9/11). Porphyria cases showed homogeneous and granular C3d (11/11) and C4d (7/11), mirroring the vascular immunoglobulin and C5b-9 by DIF. All cases of urticarial (5), leukocytoclastic (6), and lymphocytic (1) vasculitis exhibited prominent mural C3d and C4d in BV, whereas Henoch-Schönlein purpura (10/10) showed primarily mural BV C3d without C4d, with IgA by DIF. Three cases of relapsing polychondritis showed C3d and C4d within chondrocyte nuclei (3/3), in contrast to negative staining in chondrodermatitis nodularis helicis (0/2). Hypersensitivity reactions were negative for C3d and C4d.

LIMITATIONS

The small sample size in each category is a limitation. The lack of literature precedent with regard to immunohistochemical assessment of extracellular antigens on paraffin-embedded tissue in skin samples is another limitation of this study.

CONCLUSIONS

When correlated with the light microscopic and clinical findings, the C3d and C4d assay has significant application in the assessment of select inflammatory skin diseases including vasculopathic conditions, collagen vascular disease, and autoimmune vesiculobullous disorder. It may prompt further DIF testing or, in some instances, may even define a reasonable substitute for DIF and/or add to the morphologic assessment of a biopsy specimen submitted for routine light microscopic assessment primarily in the setting of autoimmune vesiculobullous disease and collagen vascular disease.

Activation of intrarenal complement system in mouse model for chronic cyclosporine nephrotoxicity

PURPOSE

Local activation of the complement system plays a role in target organ damage. The aim of our study was to investigate the influence of cyclosporine (CsA)- induced renal injury on the complement system in the kidney.

MATERIALS AND METHODS

Mice fed a low salt (0.01%) diet were treated with vehicle (VH, olive oil, 1 mL/kg/day) or CsA (30 mg/kg/day) for one or four weeks. Induction of chronic CsA nephrotoxicity was evaluated with renal function and histomorphology. Activation of the complement system was assessed through analysis of the expression of C3, C4d, and membrane attack complex (MAC), and the regulatory proteins, CD46 and CD55. CsA treatment induced renal dysfunction and typical morphology (tubulointerstitial inflammation and fibrosis) at four weeks.

RESULTS

CsA-induced renal injury was associated with increased the expression of C3, C4d, and MAC (C9 and upregulation of complement regulatory proteins (CD 46 and CD55). Immunohistochemistry revealed that the activated complement components were mainly confined to the injured tubulointerstitium.

CONCLUSION

CsA-induced renal injury is associated with activation of the intrarenal complement system.