Profiling the CD8low phenotype, an alternative career choice for CD8 T cells during primary differentiation.
A CD8+ T cell of naive phenotype has multiple career choices during its primary differentiation into an effector cell population. One of these career options is becoming a CD8low T cell. We have previously shown by in vitro studies that CD8low T cells have lost expression of CD8 surface protein and mRNA and are poorly cytolytic. In line with poor cytolytic function, CD8low T cells express low levels of perforin and granzyme B and C, mediators of the granule-exocytosis machinery. However, CD8low T cells express IFN-gamma and substantial amounts of IL-4, the signature cytokines of type 1 and type 2 T-cell polarization, respectively. Here, we argue that the CD8low phenotype is an alternative career choice for any naive CD8+ T cell during primary activation but that the probability of choosing this option is greatly enhanced by both IL-4 and strong activation conditions. CD8low T cells have downregulated CD8 alpha/beta heterodimers and no preferential CD8 alpha/alpha homodimer expression. As shown by anti-CD8 Ab blocking experiments, surface CD8 substantially contributes to the CD8 T cell's effector function (i.e. cytokine expression and cytolytic activity). The distinct effector profile of CD8low T cells gives an example of the complexity of different CD8 T cell careers during primary effector differentiation.
Cooperative Research Centre for Vaccine Technology, Queensland Institute of Medical Research, Brisbane 4006, Australia. norbertK@qimr.edu.au
Norbert
N
Kienzle
Adriana
A
Baz
Anne
A
Kelso
D000818:Animals; D016827:CD8 Antigens / Q000378:metabolism*; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology* / Q000378:metabolism*; D002454:Cell Differentiation; D006801:Humans; D008213:Lymphocyte Activation
D016827:CD8 Antigens; C431698:CD8alpha antigen; C477867:CD8beta antigen