The evolution of the interstitial infiltrate in rejecting rat renal allografts: With particular reference to the production of gamma-interferon

This study aimed to examine the evolution of the leucocytic infiltrate in rat renal allografts in the first 5 days of rejection. Immunohistology was used to assess the absolute numbers of infiltrating leucocytes in the rejecting allografts. The total infiltrate approximately doubled daily from day 1 through to day 4 (370 ± 15 total leucocytes/mm² of tissue on day 1 vs 5055 ± 135 on day 4, p<0.05 for all days) and increased only a minor degree on day 5 (5485± 535 leucocytes/mm², p = n.s.). CD4 positive cells predominated until day 3, after which time CD8 positive cells greatly outnumbered CD4 positive cells (CD4.CD8 ratio day 3 1.83 vs day 5 0.53, p<0.05). Gamma-interferon was positive in T cells on day 2 (73% of all T cells) and was slightly positive on day 3 (5% of all T cells) but was negative on days 4 and 5. Activation markers such as IL-2Rs increased markedly from day 3. These findings favour a pivotal role for CD4 positive cells in the early phase of rejection and suggest that the early release of lymphokines by these cells is associated with the recruitment of CD8 positive cells to the allograft and the activation of those leucocytes present.