Constitutive expression of interleukin 4 in vivo does not lead to the development of T helper 2 type CD8+ T cells secreting interleukin 4 or interleukin 5

Interleukin 4 (IL-4) has been shown to commit CD8(+) T cells to a T helper (Th) 2 functional phenotype in vitro. To study the effects of IL-4 on CD8(+) T cell development in vivo we analysed the CD8(+) T cell phenotype in mice constitutively expressing IL-4. Purified CD8(+) T cells from uninfected or flu infected IL-4 transgenic (tg) animals produced no detectable IL-4 or IL-5 after in vitro stimulation on anti-CD3 coated plates. However, CD8(+) T cells from IL-4 tg mice could be converted into IL-4 and IL-5 producers in vitro in the presence of exogenous added IL-4, showing that these cells were still responsive to IL-4. IL-4 tg mice also showed a delay in influenza virus clearance from the lung, which was probably due to the observed reduction of total CD8(+) T cell numbers in the IL-4 tg animals since IL-4 tg CD8(+) T cells showed normal levels of influenza-specific cytotoxicity in comparison to controls. Taken together these results suggest that CD8(+) T cells are not necessarily switched to a Th2 phenotype by the presence of IL-4 and that some other factor(s) may be important in the switch process of CD8(+) T cells in vivo, since the addition of IL-4 during CD8(+) T cell activation in vitro leads to Th2 type CD8(+) T cells secreting IL-4 and IL-5. (C) 1999 Elsevier Science B.V. All rights reserved.