Two different subsets of T cells, Th1 and Th2 cells, have been demonst
rated to secrete different profiles of cytokines and to influence vari
ous infections in different ways, Whereas cytokines secreted by Th1 ce
lls, particularly gamma interferon, promote the generation of cell-med
iated immunity, Th2 cells and their cytokines (interleukin-4 [IL-4], I
L-5, IL-10, and IL-13) have been shown to function in recovery from pa
rasitic infections and in antibody responses, In this study, we analyz
ed the effects of the dominant Th2 cytokine, IL-4, on immunity to viru
s infection, We assessed the effects of IL-4 on both secondary immune
responses by an adoptive transfer assay and primary immune responses b
y in vivo treatment of influenza virus-infected mice with IL-4. The re
sults demonstrated that IL-4 can function to inhibit antiviral immunit
y at both stages, We found that IL-4 treatment of sensitized cells dur
ing secondary stimulation in vitro had little effect on their ability
to lyse virus-infected target cells in a Cr-51 release assay, Neverthe
less, the clearance of influenza A/PR/8/34 (H1N1) virus from the lungs
of infected BALB/c mice was significantly delayed after the transfer
of virus-specific T cells secondarily stimulated in the presence of IL
-4 in comparison to virus clearance in recipients of cells stimulated
in the absence of IL-4, In contrast to the adoptive transfer results,
the treatment of PR8 virus-infected mice,vith IL-4 during primary infe
ction greatly suppressed the generation of cytotoxic T-cell precursors
, as assessed by secondary stimulation in vitro, In addition, culture
supernatants of secondarily stimulated spleen cells from IL-4-treated
mice contained significantly less gamma interferon and more IL-4 than
did spleen cells from controls, More importantly, the treatment of mic
e with IL-4 resulted in an extremely significant delay in virus cleara
nce, Thus, IL-4 can inhibit both primary and secondary antiviral immun
e responses.