Infiltration of the kidney by αβ and γδ T cells: Effect on progression in IgA nephropathy. We have studied renal biopsies from three groups of patients to determine if αβ T cells or γδ cells are present, and whether their presence is correlated with disease progression in IgA nephropathy (IgAN). Group one comprised thin basement membrane disease biopsies (non-immunological control, N = 7); group two were patients with IgAN and stable renal function one year following biopsy (stable, N = 7); and group three were IgAN patients with rapidly declining renal function after one year (progressive, N = 7). Immunohistochemical staining using monoclonal antibodies (CD3, TcRβ, TcRδ) and molecular studies utilizing polymerase chain reaction amplification of cDNA transcribed from biopsy RNA, with primers specific for either the αβ TcR or γδ TcR, were undertaken. On immunohistochemistry a significant increase in CD3+cells in progressive biopsies was seen (vs. control P = 0.002, vs. stable P = 0.002). The progressive biopsies infiltrate consisted of both αβ TcR (vs. control P = 0.001, vs. stable P = 0.003) and γδ TcR cells (vs. control P = 0.01). The RNA study demonstrated an increase in TcR Cα transcription in the progressive (vs. control P = 0.003) biopsies. Increased TcR Cδ transcription was seen in the progressive group (vs. control P = 0.01, vs. stable P = 0.02). We confirm that the presence of lymphocytes in IgAN biopsies predicts progressive disease. While αβ T cells are found in both stable and progressive disease, the presence of γδ T cells is only associated with progressive IgAN.