Scintigraphy and immunohistology of antimyosin-fab during graft rejection

Up to now, the cellular localization pattern of monoclonal antimyosin antib odies (AMA) during acute rejection has not been described. Focused on this the authors made immunohistochemical and scintigraphic studies (AMS) with A MA in an animal transplantation model. Heterotopic cervical heart transplan tation was performed in 12 mongrel dogs. Immunosuppression consisted of tri ple drug therapy. As standard the grafts were examined by daily transmural biopsies and routine histology. Dependent on the daily biopsy results, 0.5 mg of indium 111 (In-111)-labeled AMA-Fab was injected. Subsequently every 2 hours transmural biopsy cylinders were taken out of the right ventricle a nd examined in indirect peroxidase staining technique. Forty-eight hours af ter AMA injection, scintigraphy in single photon emission computed tomograp hy (SPECT) technique (AMS) was carried out and the heart-to-lung ratio (H/L -ratio) was calculated. The immunohistochemical maximum of AMA accumulation could be found 20 to 72 hours after AMA injection. This means that a scint igraphic examination should be done earlier than 20 hours and later than 3 days after injection. Dependent on the grades of bioptic rejection diagnosi s a specific morphologic AMA localization was seen (grade II-II intercellul ar and slightly intracellular detection of A, grade III strongly intracellu lar and in particular perinuclear accumulation of the antibody, p < 0.01). Moreover, the authors found a good correlation between scintigraphic H/L-ra tio results and the corresponding histologic findings (grade I: H/L = 2.1 /- 0.2; grade II: H/L = 3.1 +/- 0.2; grade III: H/L = 3.5 +/- 0.3; n = 19; p < 0.02). The recently described positive AMS scans even in cases of mild rejection seem to be subject to an intercellular AMA localization. This typ ical AMA morphology during mild rejection favors the theory of the pore-for ming protein allowing the efflux of myosin fragments as effector mechanism of cytotoxic lymphocytes in the early phase of acute rejection. The immunoh istochemical AMA examination could explain the present discrepancy between positive AMS results of an intracellular protein in cases of mild or modera te acute rejection when visible cellular damage in the corresponding routin e histology is absent.