Antithymocyte globulin is associated with complement deposition in cardiac transplant biopsies.

The study investigates the effect of antithymocyte globulin treatment on human cardiac transplants, revealing that this treatment is linked with complement deposition correspondingly leading to potential immune reactions.

Introduction and Methodology

• The researchers delved into the effects of antithymocyte globulin (ATGAM), a treatment typically prescribed to patients who have recently undergone heart transplants, to prevent organ rejection.
• The researchers hypothesized that ATGAM may cause complement deposition, a process triggering the immune reaction in the grafted heart tissues.
• To validate this hypothesis, they examined frozen tissue samples from 75 heart transplant patients spanned out over 5 years, with nine of these patients having been treated with ATGAM.
• The tissue samples were tested for the presence of C4d, an immune marker indicative of complement activation, and horse Immunoglobulin G (IgG), an antibody contained in the ATGAM preparation.

Findings

• The results showed that all nine patients treated with ATGAM showed evidence of horse IgG and C4d deposition, suggesting an immune reaction has occurred.
• Immunofluorescent staining further confirmed that the presence of horse IgG and the activation marker C4d coincided. Biopsies taken before ATGAM treatment failed to show staining for either compound, reinforcing further the idea of their relationship with ATGAM treatment.
• Surprisingly, seven control patients exhibited the presence of C4d without horse IgG, indicating that C4d deposition is not exclusively related to ATGAM therapy.
• Interestingly, despite the evident immune reactions, most of the ATGAM-treated patients did not show histologic signs of organ rejection. However, samples revealed signs of myocyte damage and macrophage infiltration, revealing other potential risks associated with ATGAM use.

Conclusion

• This study underscores a notable link between prophylactic antithymocyte globulin treatment and subsequent deposition of horse IgG and activation of the immune response within transplants.
• Further research is required to better understand how these immune reactions might influence the long-term outcome of heart transplants and to optimize the therapeutic use of ATGAM.