Predominance of TH2 cells and plasma cells in polyoma virus nephropathy: a role for humoral immunity?

The differential diagnosis of T cell-mediated rejection (TCMR) and BK-virus nephropathy (BKVN) in renal transplant biopsies is notoriously difficult. Therefore, attempts were made to differentiate between the two by characterizing the immune cell infiltrate. Using immunohistochemistry, the distribution of immune cell (sub)populations such as CD4(+) T helper (TH), TH1, TH2, CD8(+) cytotoxic T cells, regulatory T cells, B cells, plasma cells and follicular dendritic cells was determined in a total of 38 renal biopsy specimens. In addition, the expression of the HLA class I antigen presentation machinery (APM) components was investigated. In general, the frequency of T cells was higher than B cells, and TH cells outnumbered cytotoxic T cells with a predominance of TH2 over TH1 cells. In BKVN, a significantly higher number of plasma cells was observed (P = .028), and interstitial fibrosis and tubular atrophy was more pronounced in BKVN (P = .007) compared to TCMR. The expression of components of the HLA class I APM was not affected by the infection with BK virus compared to TCMR. These findings indicate a TH2 shift in renal transplants in the context of alloreactive and virus-induced inflammation maybe as a consequence of immunosuppression, which usually targets T cell reaction. The predominance of plasma cells might underline an important role of humoral immunity in BKVN. Moreover, BK virus does not seem to modulate the expression of HLA class I APM as a strategy of immune evasion.