Renal allograft rejection: The development and function of tubulitis

After renal transplantation a population of activated allospecific T cells can infiltrate the tubules during acute rejection. These T cells, which are predominantly CD8+, migrate under the influence of chemokines produced by tubular epithelial cells, and target the tubular epithelium specifically. Within the tubular epithelial microenvironment they encounter a range of cytokines including TGF β 1 , which stimulates induction of the α E / β 7 integrin (CD103), α E / β 7 integrin stabilises T cell interaction with E-cadherin on the tubular epithelial cells. The close association maintained between donor antigen-specific intratubular T cells and antigen-expressing donor epithelial cells may result in damage to the tubular epithelial cells during acute rejection. However, it is possible that IL-15, which is also produced by tubular epithelial cells, can support long-term survival of a donor antigen-specific memory-like population of CD8+ T cells. Thus, focal lesions may be created that could promote tubulo-interstitial changes including fibrosis and, in the long term, cause chronic graft dysfunction. Tubulitis is clearly fundamental to defining the pathology of acute rejection. In this review we suggest that this inflammatory process can also result in the development of a long-lived population of immune cells within the tubules that could play an active role in promoting the development of chronic graft pathology. Therefore, factors that promote the recruitment and survival of allospecific lymphocytes within the tubular microenvironment are important targets to be considered for therapeutic intervention in both acute and chronic renal allograft rejection.