Antibody-mediated rejection in human cardiac allografts: evaluation of immunoglobulins and complement activation products C4d and C3d as markers

Abstract

Antibody-mediated rejection (AMR) in human heart transplantation is an immunopathologic process in which injury to the graft is in part the result of activation of complement and it is poorly responsive to conventional therapy. We evaluated by immunofluorescence (IF), 665 consecutive endomyocardial biopsies from 165 patients for deposits of immunoglobulins and complement. Diffuse IF deposits in a linear capillary pattern greater than 2+ were considered significant. Clinical evidence of graft dysfunction was correlated with complement deposits. IF 2+ or higher was positive for IgG, 66%; IgM, 12%; IgA, 0.6%; C1q, 1.8%; C4d, 9% and C3d, 10%. In 3% of patients, concomitant C4d and C3d correlated with graft dysfunction or heart failure. In these 5 patients AMR occurred 56-163 months after transplantation, and they responded well to therapy for AMR but not to treatment with steroids. Systematic evaluation of endomyocardial biopsies is not improved by the use of antibodies for immunoglobulins or C1q. Concomitant use of C4d and C3d is very useful to diagnose AMR, when correlated with clinical parameters of graft function. AMR in heart transplant patients can occur many months or years after transplant.

Figure 1

Immunofluorescence microscopy of a heart biopsy from patient 5 in Table 3, 68 months after heart transplant during the episode of antibody-mediated rejection plotted in Figure 2A. IgM deposits (3+) are present in granular pattern around capillaries. Note the absence of deposits in perimyocyte location. (60×) (FITC anti-IgM). C1q deposits are barely detectable in the capillaries (60×) (FITC anti-C1q). C4d staining shows intense linear deposits in the capillary endothelium (cross sections as well as longitudinally oriented capillaries are shown) (60×) (FITC anti-C4d). C3d deposition is clearly positive in same linear pattern around capillaries, identical to that shown for the C4d deposits. (60×) (FITC anti-C3d).

Figure 2

Example of developing antibody-mediated rejection (AMR) in a heart transplant patient (patient 1 from Table 3). (A) At 52 months after her 2nd transplant the ejection fraction (EF) began to drop. At 59 weeks while the EF continued to decrease, there was an increase in right atrial pressure (RA) and pulmonary capillary wedge pressures (PCW). (B) At this time there was also a change in the complement deposition grading in her endomyocardial biopsies and donor-specific antibodies were documented in this patient, which overlapped in time with the C4d and C3d deposits in the Endomyocardial biopsy. Thus, the hemodynamic changes correlate with pathologic evidence of AMR

Figure 3

Time of appearance of complement deposits in endomyocardial biopsies counted from the time of transplantation.