A new mouse laryngeal transplantation rejection grading system

Objectives/Hypothesis: Development of a rat laryngeal transplantation model allowed for the first total human laryngeal transplantation by the senior author in 1998. In an effort to further our knowledge of the immune system's role in laryngeal rejection, a change to the mouse model was required. Prior to initiating immunosuppressive research protocols, a reliable mouse larynx rejection classification had to be established. Study Design: Animal study. Methods: Thirty-one mouse laryngeal transplants (C57 BL/6 donors to C3H recipients) were performed and allowed to reject. Six time points were evaluated histologically: 1, 3, 5, 7, 9, and 15 days post-transplant. Eight anatomic sites were evaluated and assigned a point value. A linear regression model was constructed using the group number as the response and the scores from the eight histological criteria as predictors. Severity classifications were determined by observing patterns in the sum of scores of variables found to be significant contributors. Group 1 was normal; group 2, minimal rejection; groups 3, 4, and 5, moderate rejection; and group 6, severe rejection. Results: All mice survived the transplants. Of the observed histological changes, cartilage, fat, muscle, and magnitude of lymphocytic infiltration significantly correlated with rejection severity. The rejection model created demonstrated 100% accuracy in predicting the severity classification for the 31 specimens in the study. Conclusions: The model established provides an accurate and reliable way to classify rejection severity in mice receiving laryngeal allografts. This sets the stage for future advanced study of manipulating the immune system as a mechanism for establishing allograft tolerance.