Polyclonal IgG4 Hypergammaglobulinemia Associated with Lymphadenopathy and Renal Disease: A Novel Syndrome.

Marked polyclonal IgG4 hypergammaglobulinemia has exceptionally been reported. Here we report on two patients who presented an unique syndrome including a predominant and massive increase in serum levels of the IgG4 subclass. Clincal, biological and pathological data were described. Production of IgG4 by patients’ peripheral blood lymphocytes was studied, as well as the capacity of patients’ sera and T lymphocytes to induce IgG4 production by normal B cells. The possible involvement of IL4 and IL13 in the increased IgG4 production was also investigated. The two patients had anemia, lymphadenopathy, renal manifestations and a marked polyclonal IgG4 hypergammaglobulinemia leading to hyperviscosity syndrome in one case. The IgG4-producing cell percentage was significantly increased in both cases. By contrast with normal sera, both patients’ sera significantly increased the IgG4-producing cell percentagae when incubated with CD40-stimulated normal B lymphocytes. Similar effects were obtained with the culture supernatants of patients’ activated T cells. IL4 and IL13 serum concentrations were normal in the two patients. Anti-IL4 and/or anti-IL13 antibodies were unable to antagonize the IgG4 synthesis. The increased IgG4 production was found to be mediated by soluble, heat-resistant factor(s) that did not require the Stat6 signaling pathway. We described here a novel syndrome characterized by a significantly increased IgG4 production, mediated by soluble, heat-stable factor(s) most probably secreted by activated T cells, and distinct from IL4 and IL13.