Increase of IgA-specific switch T cells in patients with IgA nephropathy.

Enumeration and functional analysis of CD4+ T cells with receptors for the Fc portion of IgA (i.e. T alpha 4 cells) in the peripheral blood of patients with IgA nephropathy, their relatives and age-matched controls were performed to elucidate polyclonal activation of IgA production in this disease. Enumeration of T alpha 4 cells was performed by a fluorescence activated cell sorter, and functional analysis was carried out by separation of T alpha 4 cells, and IgM-, IgA- and IgG-bearing lymphocytes using panning methods followed by cultures of these cells for 7 days with pokeweed mitogen. There was a significant increase in the amount of peripheral blood T alpha 4 cells in patients with IgA nephropathy and their relatives. T alpha 4 cells specifically enhanced the switch of IgM-bearing cells to IgA-bearing cells, and this switch activity was inhibited by addition of human myeloma IgA. It is suggested that T alpha 4 cells may be responsible for polyclonal activation of IgA production in IgA nephropathy.