Helper T cells without CD4: control of leishmaniasis in CD4-deficient mice.

Expression of either the CD4 or CD8 glycoproteins discriminates two functionally distinct lineages of T lymphocytes. A null mutation in the gene encoding CD4 impairs the development of the helper cell lineage that is normally defined by CD4 expression. Infection of CD4-null mice with Leishmania has revealed a population of functional helper T cells that develops despite the absence of CD4. These CD8- alpha beta T cell receptor+ T cells are major histocompatibility complex class II-restricted and produce interferon-gamma when challenged with parasite antigens. These results indicate that T lymphocyte lineage commitment and peripheral function need not depend on the function of CD4.