A limiting-dilution analysis of activated circulating B cells in Crohn's disease.

In the present study the spontaneous in vitro production of immunoglobulins G, A, and M by peripheral mononuclear cells was evaluated, in patients with Crohn's disease, in relation to the state of B-cell activation and further characterized by limiting-dilution analysis. A total of 25 patients with Crohn's disease and 10 healthy controls was studied. The proportion of the transferrin receptor-bearing cells in the B7+ subset was higher in active Crohn's disease patients than in either those with quiescent disease or controls. There was a significant rise in the in vitro IgG, IgM, and IgA production in patients with untreated active Crohn's disease compared to either those with untreated quiescent disease or controls. When patients were followed up from the active phase to clinical remission, a significant decrease in the production of IgG and IgM was observed. IgA levels also showed a decrease, although not reaching statistical significance. When the Ig production was analyzed by limiting dilution, no difference was observed between patients and controls in terms of either precursor frequency of Ig-producing cells or patterns of frequency distribution. In both patients and controls a biphasic limiting-dilution profile was observed. This study shows that a significant B-cell activation is present in Crohn's disease patients, which is accompanied by an increase in immunoglobulin production. This study also indicates that in Crohn's disease the increased immunoglobulin production is related to an augmented B-cell clone size rather than to an increased precursor frequency.