IL-4 enhances long-term survival of CD28-deficient T cells.

CD28 signaling is critical for IL-2 production by established Th1 clones, but CD28 does not appear to play a role in the activation of established Th2 clones. To determine the role of CD28 in the generation of polarized T cells, clones were derived using cells from CD28-deficient (CD28-/- mice, which had been bred with mice that express the DO11.10 transgene, a CD4+ TCR-alphabeta receptor that recognizes OVA peptide 323-339 bound to I-Ad. Most T cell clones derived from CD28+/+ mice survived multiple stimulations, while T cell clones derived from CD28-/- mice survived only if they were derived initially in the presence of IL-4 or both IL-2 and IL-4. Signaling through the CD28 molecule did not appear to be important in the initial activation of T cell clones, as the precursor frequency of clones derived from normal (CD28+/+) and CD28-/- mice was similar. Primary stimulation in the presence of IL-4 increased cell number and viability of both CD28+/+ and CD28-/- T cells in primary culture. However, the survival of CD28-/- cells is more dependent on IL-4 than is the survival of CD28+/+ cells. The continued presence of anti-IL-4 mAb dramatically decreased the number of viable cells in the CD28-/- cultures but had little effect on the viability of the CD28+/+ clones. Thus, initial culture with IL-4 allows the isolation of CD28-/- T cell clones that produce IL-4. In these clones, IL-4 acts as both an autocrine growth and survival factor.