Evidence of follicular T-cell implication in a case of IgG4-related systemic disease with interstitial nephritis.

IgG4-related systemic disease is a protean disorder that covers a wide variety of lesions. We report on a patient with tubulointerstitial nephritis, lymphadenopathies, sialadenitis and retroperitoneal fibrosis. The salivary gland and kidney interstitium were infiltrated with B lymphocytes and T lymphocytes and IgG3(+) and IgG4(+) plasma cells. The overexpression of IgG1 and IgG3, in addition to IgG4, the unusual abundance of interfollicular plasma cells and CD4(+) T cells in germinal centres of lymph nodes, and the dramatic response to rituximab point to possible roles of follicular helper T cells in enhancing a skewed B-cell terminal maturation and of CD20(+) B cells in disease progression.