To clarify the effect of bucillamine, an antirheumatic drug related to D-penicillamine, on the development of human Th1 and Th2 cells in vitro.
Peripheral blood mononuclear cells (PBMC) or purified CD4+ T cells were subjected to the priming culture in which cells were stimulated with anti-CD3 and anti-CD28 monoclonal antibodies for 3 days and expanded for 4 days in the presence of interleukin-2. Cytokine production by the generated cells was determined on a flow cytometer using intracellular cytokine staining. The effects of bucillamine were determined by adding it for the first 3 days of the priming culture.
Bucillamine decreased the frequency of interferon-gamma (IFN-gamma) producing CD4+ T cells among generated CD4+ T cells after the priming culture of PBMC, although D-penicillamine did not. This effect of bucillamine was independent of hydrogen peroxide since it was not reversed by a catalase treatment. One of the bucillamine metabolites, SA981, which exerts its effects by a hydrogen peroxide-independent mechanism, decreased the frequency of IFN-gamma producing CD4+ T cells more potently than bucillamine. Bucillamine reduced the frequency of Th1 cells after the priming culture of purified CD4+CD45RO- T cells, indicating that bucillamine exerts the effect in the absence of monocytes or B cells.
Bucillamine directly acts on CD4+CD45RO- T cells to suppress Th1 cell development by a hydrogen peroxide-independent mechanism. This previously unknown action may explain the in vivo effect of bucillamine in the treatment of rheumatoid arthritis.