Rapid serologic diagnosis of serum sickness from antithymocyte globulin therapy using enzyme immunoassay.

Although the use of antithymocyte globulin/antilymphocyte serum (ATG/ALS) has been shown to be beneficial in treating renal allograft rejection, the incidence and nature of serum sickness reactions following such treatment have received limited attention. In the setting of rejection or infection, the diagnosis of serum sickness is often difficult on clinical grounds, and biopsy may be an undesirable means of obtaining documentation. A sensitive enzyme-linked immunosorbent assay (ELISA) was developed to detect antibodies against ATGAM (Upjohn) and was utilized in 35 patients treated for rejection with ATGAM following clinical unresponsiveness to bolus methylprednisolone therapy. Serum sickness was diagnosed clinically in 7 of these patients (20%) during or immediately following ATGAM therapy. Significant titers of anti-ATGAM antibody were found in these 7 cases, as well as 5 additional cases (14%). Upon retrospective review, the diagnosis of serum sickness was also made in each of these 5 additional cases based upon the immunopathologic detection of horse immunoglobulin deposits in vessels of tissue (lung or kidney) examined. In 2 other cases where serologic testing was negative, there was some clinical suggestion of serum sickness that could not be documented pathologically. ELISA for anti-ATGAM antibodies was negative in testing 46 control patients and pooled normal sera. In one case, retrospective testing of pre-ATGAM therapy serum samples showed significant antihorse antibodies. Despite a negative skin test prior to administration, this patient developed symptoms of serum sickness 15 days after the onset of ATGAM therapy. Extremely high titers of antibody were detected 5 days earlier (10 days posttherapy), and the presence of horse immunoglobulin immune complexes in the kidney was documented following graft loss that occurred within 4 weeks. These findings indicate (1) serologic testing for anti-ATGAM antibodies using a sensitive ELISA method provides a quick, inexpensive, noninvasive means for the presumptive diagnosis of serum sickness in complicated clinical situations, and (2) screening of patient sera prior to administration of ATGAM may be useful in avoiding potential serum sickness reactions.