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From the * Department of Medicine, Committee on Immunology and Gwen Knapp Center for Lupus
and Immunology Research, University of Chicago, Chicago, Illinois 60637; and Naive CD4+ T helper cells (Th) differentiate into one of two well-defined cell types during
immune responses. Mature Th1 and Th2 cells regulate the type of response as a consequence of
the unique cytokines that they secrete. CD4 serves a prominent role in potentiating antigen
recognition by helper T cells. We have examined the role of CD4 in peripheral T cell differentiation by studying helper T cells from mice with a congenital defect in CD4 expression. After
protein immunization or infection with Leishmania major, CD4-deficient mice were incapable
of mounting antigen-specific Th2 responses, but retained their Th1 potency. CD4-deficient, T cell
receptor transgenic T cells were also incapable of Th2 differentiation after in vitro activation.
Expression of a wild-type CD4 transgene corrected the Th2 defect of CD4-deficient mice in
all immune responses tested. To investigate the role of the cytoplasmic domain, mice reconstituted with a truncated CD4 molecule were also studied. Expression of the tailless CD4 transgene could not rescue the Th2 defect of CD4-deficient mice immunized with protein or
CD4-deficient transgenic T cells activated in vitro, raising the possibility that the cytoplasmic
domain of CD4 may influence Th2 generation. Expression of the tailless transgene was, however, capable of restoring Th2 development in CD4-deficient mice infected with L. major or
CD4-deficient transgenic T cells activated in the presence of recombinant IL-4, demonstrating
that the cytoplasmic domain is not absolutely required for Th2 development. Together, these
results demonstrate a previously undescribed role of the CD4 molecule. The requirement for
CD4 in Th2 maturation reflects the importance of molecules other than cytokines in the control of helper T cell differentiation.
Department of
Microbiology and Immunology, University of California, San Francisco, San Francisco, California
94143
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