CD28 ACTIVATION PROMOTES TH2 SUBSET DIFFERENTIATION BY HUMAN CD4(+) CELLS

Ligation of CD28 provides a costimulatory signal to T cells necessary for their activation resulting in increased interleukin (IL)-2 product ion in vitro, but its role in IL-4 and other cytokine production and f unctional differentiation of T helper (Th) cells remains uncertain. We studied the pattern of cytokine production by highly purified human a dult and neonatal CD4(+) T cells activated with anti-CD3, phorbol 12-m yristate 13-acetate (PMA) and ionomycin, or phytohemagglutinin (PHA) i n the presence or absence of anti-CD28 in repetitive stimulation-rest cycles. Initial stimulation of CD4(+) cells with anti-CD3 (or the mito gens PHA or PMA+ionomycin) and anti-CD28 monoclonal antibodies induced IL-4, IL-5 and interferon-gamma (IFN-gamma) production and augmented IL-2 production (6- to 11-fold) compared to cells stimulated with anti -CD3 or mitogen alone. The anti-CD28-induced cytokine production corre sponded with augmented IL-4 and IL-5 mRNA levels suggesting increased gene expression and/or mRNA stabilization. Most striking, however, was the progressively enhanced IL-4 and IL-5 production and diminished IL -2 and LFN-gamma production with repetitive consecutive cycles of CD28 stimulation. The enhanced Th2-like response correlated with an increa sed frequency of IL-4-secreting cells; up to 70 % of the cells produce d IL-4 on the third round of stimulation compared to only 5 % after th e first stimulation as determined by ELISPOT. CD28 activation also pro moted a Th2 response in naive neonatal CD4(+) cells, indicating that T h cells are induced to express a Th2 response rather than preferential expansion of already established Th2-type cells. This CD28-mediated r esponse was IL-4 independent, since enhanced IL-5 production with repe titive stimulation cycles was not affected in the presence of neutrali zing anti-IL-4 antibodies. These results indicate that CD28 activation may play an important role in the differentiation of the Th2 subset i n humans.